Bonding wire for semiconductor device

ABSTRACT

A bonding wire for a semiconductor device includes a Cu alloy core material and a Pd coating layer formed on a surface thereof. Containing an element that provides bonding reliability in a high-temperature environment improves the bonding reliability of the ball bonded part in high temperature. Furthermore, making an orientation proportion of a crystal orientation &lt;100&gt; angled at 15 degrees or less to a wire longitudinal direction among crystal orientations in the wire longitudinal direction 30% or more when measuring crystal orientations on a cross-section of the core material in a direction perpendicular to a wire axis of the bonding wire, and making an average crystal grain size in the cross-section of the core material in the direction perpendicular to the wire axis of the bonding wire 0.9 to 1.5 μm provides a strength ratio of 1.6 or less.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present Application is a continuation of U.S. patent applicationSer. No. 15/515,508, filed Mar. 29, 2017, which is the U.S. NationalPhase of PCT/JP2016/064926 filed May 19, 2016, which claims priority toJapanese Patent Application No. 2015-120509 filed Jun. 15, 2015, andInternational Patent Application No. PCT/JP2015/070861 filed Jul. 22,2015. The subject matter of each is incorporated herein by reference inentirety.

TECHNICAL FIELD

The present invention relates to a bonding wire for a semiconductordevice used to connect electrodes on a semiconductor device and wiringof a circuit wiring board such as outer leads.

BACKGROUND ART

Currently, as a bonding wire for a semiconductor device connectingbetween electrodes on a semiconductor device and outer leads(hereinafter referred to as a “bonding wire”), thin wires with a wirediameter of about 15 to 50 μm are mainly being used. A method forbonding the bonding wire is generally a thermal compressive bondingtechnique with the aid of ultrasound, which uses a general-purposebonder, a capillary tool used for bonding by passing the bonding wiretherethrough, and the like. A bonding process of a bonding wire iscarried out by heating and melting a tip of wire by arc heat input toform a ball (FAB: free air ball) through surface tension; crimp-bondingthe ball part onto an electrode of the semiconductor device heatedwithin a range of 150 to 300° C. (hereinafter referred to as “ballbonding”); forming a loop; and finally crimp-bonding a wire part onto anelectrode of the outer lead (hereinafter referred to as “wedgebonding”). As bonding counterparts of the bonding wire, an electrodestructure in which an alloy mainly containing Al is formed as a film ona Si substrate is used for the electrode on the semiconductor device,whereas an electrode structure plated with Ag or Pd is used for theelectrode of the outer lead.

Au, which has been mainly used as a material of the bonding wire, hasbeen being replaced with Cu mainly for LSI use. On the background ofrecent proliferation of electric vehicles and hybrid vehicles, needs forreplacing Au with Cu are increasing also in on-vehicle device use.

As for a Cu bonding wire, there has been proposed a wire usinghigh-purity Cu (purity: 99.99% by mass or more) (for example, PatentLiterature 1). Cu has the drawback of being more susceptible tooxidation than Au and has problems in that bonding reliability, ballformability and wedge bondability are inferior. As a method forpreventing surface oxidation of a Cu bonding wire, there has beenproposed a structure in which a surface of Cu core material is coatedwith a metal such as Au, Ag, Pt, Pd, Ni, Co, Cr and Ti (PatentLiterature 2). There has been also proposed a structure in which asurface of Cu core material is coated with Pd and a surface thereof iscoated with Au, Ag, Cu or an alloy thereof (Patent Literature 3).

RELATED ART REFERENCE Patent Literature

Patent Literature 1: JP-A-S61-48543

Patent Literature 2: JP-A-2005-167020

Patent Literature 3: JP-A-2012-36490

SUMMARY OF INVENTION Problem to be Solved by the Invention

On-vehicle devices require bonding reliability in a more rigoroushigh-temperature and high-humidity environment than general electronicdevices. In particular, the bonding longevity of a ball bonded part inwhich the ball part of the wire is bonded to the electrode is thebiggest concern.

A representative evaluation method for evaluating the bondingreliability of a ball bonded part in a high-temperature andhigh-humidity environment includes a highly accelerated temperature andhumidity stress test (HAST) (a high-temperature and high-humidityenvironment exposure test). When the bonding reliability of a ballbonded part is evaluated by HAST, a ball bonded part to be evaluated isexposed to a high-temperature and high-humidity environment with atemperature of 130° C. and a relative humidity of 85%, and then, thebonding longevity of the ball bonded part is evaluated by measuringtemporal changes in a resistance value of the bonded part or bymeasuring temporal changes in shear strength of the ball bonded part.

Further, as means for evaluating the bonding reliability of the ballbonded part in a high-temperature environment at 170° C. or more, a hightemperature storage test (HTS) is used. When the bonding reliability ofa ball bonded part is evaluated by HTS, a sample to be evaluated isexposed to a high-temperature environment, and then, the bondinglongevity of the ball bonded part is evaluated by measuring temporalchanges in a resistance value of the bonded part or measuring temporalchanges in shear strength of the ball bonded part.

As a result of investigation by the present inventors, it has beenrevealed that the bonding wire containing an element that providesbonding reliability in a high-temperature environment such as, forexample, Ni, Zn, Rh, In, Ir and Pt exhibits an improved bondingreliability of the ball bonded part in a high-temperature environment of130° C. or more, compared to the wire not containing such element.

A strength ratio is defined by the following Equation (1):Strength ratio=ultimate strength/0.2% offset yield strength.  (1)

In the wedge bonding, the bonding wire extremely becomes deformed. Whenthe wire is subjected to work hardening in the deformation, the wireafter bonding hardens, resulting in a decrease in the bonding strengthof the wedge bonding. In order to maintain the wedge bonding strength,the strength ratio defined by Equation (1) is preferably 1.6 or less.However, when the above-noted elements are contained in the wire for thepurpose of improving the bonding reliability of the ball bonded part inhigh-temperature environment, the strength ratio increased to exceed1.6. Consequently, the bonding strength of the wedge bonding decreased.

An object of the present invention is to provide a bonding wire for asemiconductor device including a Cu alloy core material and a Pd coatinglayer formed on a surface thereof, the bonding wire for a semiconductordevice being capable of improving the bonding reliability of the ballbonded part in high temperature and being capable of having the strengthratio defined by Equation (1) of 1.1 to 1.6.

Means for Solving Problem

That is, the summary of the present invention is as follows.

-   [1] A bonding wire for a semiconductor device, the bonding wire    comprising: a Cu alloy core material; and a Pd coating layer formed    on a surface of the Cu alloy core material, wherein the bonding wire    contains an element that provides bonding reliability in a    high-temperature environment, when measuring crystal orientations on    a cross-section of the core material in a direction perpendicular to    a wire axis of the bonding wire, a crystal orientation <100> angled    at 15 degrees or less to a wire longitudinal direction has a    proportion of 30% or more among crystal orientations in the wire    longitudinal direction, and an average crystal grain size in the    cross-section of the core material in the direction perpendicular to    the wire axis of the bonding wire is 0.9 to 1.5 μm.-   [2] The bonding wire for a semiconductor device according to [1],    wherein a strength ratio defined by the following Equation (1) is    1.1 to 1.6:    Strength ratio=ultimate strength/0.2% offset yield strength.  (1)-   [3] The bonding wire for a semiconductor device according to [1] or    [2], wherein a thickness of the Pd coating layer is 0.015 to 0.150    μm.-   [4] The bonding wire for a semiconductor device according to any one    of [1] to [3], further comprising an alloy skin layer containing Au    and Pd on the Pd coating layer.-   [5] The bonding wire for a semiconductor device according to [4],    wherein a thickness of the alloy skin layer containing Au and Pd is    0.050 μm or less.-   [6] The bonding wire for a semiconductor device according to any one    of [1] to [5], wherein the bonding wire contains at least one    element selected from Ni, Zn, Rh, In, Ir and Pt, and a concentration    of the at least one element in total is 0.011 to 2% by mass relative    to the entire wire.-   [7] The bonding wire for a semiconductor device according to any one    of [1] to [6], wherein the bonding wire contains one or more    elements selected from Ga and Ge, and a concentration of the    elements in total is 0.011 to 1.5% by mass relative to the entire    wire.-   [8] The bonding wire for a semiconductor device according to any one    of [1] to [7], wherein the bonding wire contains one or more    elements selected from As, Te, Sn, Sb, Bi and Se, a concentration of    the elements in total is 0.1 to 100 ppm by mass relative to the    entire wire, and Sn≤10 ppm by mass; Sb≤10 ppm by mass; and Bi≤1 ppm    by mass.-   [9] The bonding wire for a semiconductor device according to any one    of [1] to [8], wherein the bonding wire further contains at least    one element selected from B, P, Mg, Ca and La, and a concentration    of each of the at least one element is 1 to 200 ppm by mass relative    to the entire wire.-   [10] The bonding wire for a semiconductor device according to any    one of [1] to [9], wherein Cu is present at an outermost surface of    the bonding wire.-   [11] The bonding wire for a semiconductor device according to any    one of [1] to [10], wherein the Cu alloy core material contains a    metallic element of Group 10 of the Periodic Table of Elements in a    total amount of 0.1 to 3.0% by mass, and a concentration of Cu at an    outermost surface of the wire is 1 at % or more.

Effect of the Invention

The present invention can improve the bonding reliability of the ballbonded part in a high-temperature environment and can provide thestrength ratio defined by Equation (1) of 1.1 to 1.6.

EMBODIMENT FOR CARRYING OUT THE INVENTION

The bonding wire for a semiconductor device of the present inventionincludes a Cu alloy core material and a Pd coating layer formed on asurface of the Cu alloy core material. In the present invention, thebonding wire contains an element that provides bonding reliability in ahigh-temperature environment; when measuring crystal orientations on across-section of the core material in a direction perpendicular to awire axis of the bonding wire, a crystal orientation <100> angled at 15degrees or less to a wire longitudinal direction has a proportion of 30%or more among crystal orientations in the wire longitudinal direction;and an average crystal grain size in the cross-section of the corematerial in the direction perpendicular to the wire axis of the bondingwire is 0.9 to 1.5 μm.

A mold resin (an epoxy resin) as a package of a semiconductor devicecontains chlorine (Cl) in its molecular skeleton. In a high-temperatureand high-humidity environment of a temperature of 130° C. and a relativehumidity of 85% as a HAST evaluation condition, Cl in the molecularskeleton hydrolyzes and dissolves as a chloride ion (Cl⁻). In a casewhere a Cu bonding wire having no Pd coating layer is bonded to an Alelectrode, when a Cu/Al bonding interface is placed in high temperature,Cu and Al mutually diffuse, and Cu₉Al₄ as an intermetallic compound isfinally formed. Cu₉Al₄ is susceptible to corrosion by halogen andundergoes corrosion by Cl dissolved from the mold resin, leading todegradation in the bonding reliability. In a case where a Cu wire has aPd coating layer, a bonding interface between the Pd-coated Cu wire andthe Al electrode has a structure of Cu/Pd-concentrated layer/Al, wherebya formation of the Cu₉Al₄ intermetallic compound is reduced comparedwith a case of the Cu wire having no Pd coating layer, but it is stillinsufficient in a bonding reliability in a high-temperature andhigh-humidity environment required for on-vehicle devices.

In contrast, it is considered that when containing an element thatprovides bonding reliability in a high-temperature environment as in thepresent invention, a formation of a Cu₉Al₄ intermetallic compound in thebonded part tends to be further reduced.

In view of improving the bonding reliability of the ball bonded part ina high-temperature environment (especially the performance in HTS at175° C. or more), the concentration of the element that provides bondingreliability in a high-temperature environment in total relative to theentire wire is preferably 0.011% by mass or more, more preferably 0.030%by mass or more, further preferably 0.050% by mass or more, 0.070% bymass or more, 0.090% by mass or more, 0.10% by mass or more, 0.15% bymass or more, or 0.20% by mass or more. The element that providesbonding reliability in a high-temperature environment will be describedin detail below.

As described above, an strength ratio is defined by the followingEquation (1):Strength ratio=ultimate strength/0.2% offset yield strength.  (1)

In the wedge bonding, the bonding wire is extremely deformed. When thewire is subjected to work hardening in the deformation, the wire afterbonding hardens, resulting in a decrease in the bonding strength of thewedge bonding. In order to maintain favorable wedge bonding strength,the strength ratio defined by Equation (1) is preferably 1.6 or less.However, when the element that provides bonding reliability in ahigh-temperature environment is contained in an amount capable ofachieving sufficient effect for the purpose of improving the bondingreliability of the ball bonded part in high-temperature environment, thestrength ratio increased to exceed 1.6. It is considered that theelement contained in Cu as the core material caused an increase in thestrength ratio, that is, an increase in hardness. Consequently, adecrease in the bonding strength of the wedge bonding occurred. Incontrast, when the strength ratio was attempted to be reduced within thescope of a conventional method of manufacture, the strength ratio wasless than 1.1, resulting in inferior wedge bondability.

Given this situation, a crystal structure that can maintain the strengthratio of Equation (1) at a preferable range of 1.1 to 1.6 even with thebonding wire containing the element that provides bonding reliability ina high-temperature environment was studied. As a result of the study, ithas been found out that in maintaining the strength ratio of Equation(1) at the preferable range, it is important to control a crystalstructure of the core material of the bonding wire, especially (i) anorientation proportion of a crystal orientation <100> angled at 15degrees or less to a wire longitudinal direction among crystalorientations in the wire longitudinal direction when measuring crystalorientations on a cross-section of the core material in a directionperpendicular to a wire axis of the bonding wire (hereinafter, may alsobe referred to as a “<100> orientation proportion”) and (ii) an averagecrystal grain size in the cross-section of the core material in thedirection perpendicular to the wire axis of the bonding wire(hereinafter, may also be referred to as an “average crystal grainsize”). Specifically, it has been revealed that when the bonding wire ismanufactured by a normal method of manufacture, the <100> orientationproportion being 30% or more and the average crystal grain size being0.9 μm or more and 1.5 μm or less cannot be achieved simultaneously,resulting in the strength ratio of less than 1.1 or more than 1.6. Incontrast, it has been revealed that by devising a method of manufactureas described below, the orientation proportion of <100> containingangled at 15 degrees or less to a wire longitudinal direction amongcrystal orientations in the wire longitudinal direction on across-section of the core material in the direction perpendicular to thewire axis of the bonding wire can be 30% or more, and the averagecrystal grain size in the cross-section of the core material in thedirection perpendicular to the wire axis of the bonding wire can be 0.9to 1.5 μm, as a result of which the strength ratio of Equation (1) canbe 1.1 to 1.6.

If the <100> orientation proportion is 30% or more, work hardening ofthe wire along with the deformation at the time of the wedge bonding issmall, whereby the strength ratio can be 1.6 or less. However, even inthis case, if the average crystal grain size is less than 0.9 μm, the0.2% offset yield strength is high (poor in ductility), whereby thestrength ratio is less than 1.1, which is inferior in the wedgebondability. If the average crystal grain size is more than 1.5 μm, itis estimated that the <100> orientation proportion is less than 30%, andin addition, the 0.2% offset yield strength is low, whereby the strengthratio is more than 1.6, and the wedge bondability is inferior.

Even when the crystal structure of the wire fulfills the conditions, ifthe content of the element that provides bonding reliability in ahigh-temperature environment in the wire is excessively large, thestrength ratio may increase. In view of achieving the strength ratio of1.6 or less and reducing the hardening of the bonding wire to reducedegradation of the wedge bondability, the concentration of the elementthat provides bonding reliability in a high-temperature environment intotal relative to the entire wire is preferably 2.0% by mass or less,1.8% by mass or less, or 1.6% by mass or less.

As for addition of the element that provides bonding reliability in ahigh-temperature environment into the bonding wire, the effect of theinvention can be exhibited by employing either of a method of adding theelement into a Cu core material or a method of depositing the elementonto a Cu core material or a surface of wire to add the element therein.An added amount of these elements is infinitesimal and allows a widevariety of methods of addition, and the effect is exhibited by anymethod of addition so long as the element is contained.

In the bonding wire of the present invention, the thickness of the Pdcoating layer is preferably 0.015 μm or more, more preferably 0.02 μm ormore, and further preferably 0.025 μm or more, 0.03 μm or more, 0.035 μmor more, 0.04 μm or more, 0.045 μm or more, or 0.05 μm or more in viewof obtaining favorable FAB shape and in view of further improving thebonding reliability of the ball bonded part in the high-temperature andhigh-humidity environment required in on-vehicle devices. An excessivelylarge thickness of the Pd coating layer deteriorates the FAB shape, andthe thickness of the Pd coating layer is preferably 0.150 μm or less andmore preferably 0.140 μm or less, 0.130 μm or less, 0.120 μm or less,0.110 μm or less, or 0.100 μm or less.

There will be described the definition of the Cu alloy core material andthe Pd coating layer of the bonding wire. A boundary between the Cualloy core material and the Pd coating layer was determined based on aconcentration of Pd. The boundary was set to be a position at which aconcentration of Pd was 50 at %, and a region in which a concentrationof Pd was 50 at % or more was determined to be the Pd coating layer, anda region in which a concentration of Pd was less than 50 at % wasdetermined to be the Cu alloy core material. This is because if aconcentration of Pd is 50 at % or more in the Pd coating layer, therecan be expected an effect of improving characteristics from thestructure of the Pd coating layer. The Pd coating layer may contain aregion of a Pd single layer and a region having concentration gradientsof Pd and Cu in a wire depth direction. The reason why the region havingthe concentration gradients is formed in the Pd coating layer is thatatoms of Pd and Cu may diffuse through heat treatment or the like in amanufacturing process. In the present invention, the concentrationgradient refers to the fact that a degree of a change in concentrationin the depth direction is 10 mol % or more per 0.1 μm. Furthermore, thePd coating layer may contain inevitable impurities.

In the bonding wire of the present invention, a maximum concentration ofPd in the Pd coating layer is preferably 60 at % or more, and morepreferably 70 at % or more, 80 at % or more, or 90 at % or more, in viewof further obtaining the effect of the present invention. It ispreferable that the maximum concentration of Pd in the Pd coating layeris 100 at %. However, the bonding wire of the present invention canachieve the desired effect even in a case where the maximumconcentration of Pd in the Pd coating layer is less than 100 at %, e.g.,99.9 at % or less, 99.8 at % or less, 99.7 at % or less, 99.6 at % orless, 99.5 at % or less, 99.0 at % or less, 98.5 at % or less, 98 at %or less, 97 at % or less, 96 at % or less, or 95 at % or less.

In the bonding wire of the present invention, a region having aconcentration of Pd of 99.0 at % or more in the Pd coating layer mayhave a thickness of 40 nm or less, e.g., 35 nm or less, 30 nm or less,25 nm or less, 20 nm or less, 15 nm or less, 10 nm or less, or 5 nm orless.

The bonding wire of the present invention may further include an alloyskin layer containing Au and Pd on the surface of the Pd coating layer.With this configuration, the bonding wire of the present invention canfurther improve the bonding reliability and can further improve thewedge bondability.

There will be described the definition of the alloy skin layercontaining Au and Pd of the bonding wire. A boundary between the alloyskin layer containing Au and Pd and the Pd coating layer was determinedbased on a concentration of Au. The boundary was set to be a position atwhich a concentration of Au was 10 at %, and a region in which aconcentration of Au was 10 at % or more was determined to be the alloyskin layer containing Au and Pd, and a region in which a concentrationof Au was less than 10 at % was determined to be the Pd coating layer.Even in the region in which a concentration of Pd was 50 at % or more, aregion in which Au was present at 10 at % or more was determined to bethe alloy skin layer containing Au and Pd. These determinations arebecause if a concentration of Au falls within the range mentioned above,there can be expected an effect of improving characteristics from thestructure of the Au skin layer. The alloy skin layer containing Au andPd is an Au—Pd alloy and contains a region having concentrationgradients of Au and Pd in the wire depth direction. The reason why theregion having the concentration gradients is formed in the alloy skinlayer containing Au and Pd is that atoms of Au and Pd diffuse throughheat treatment or the like in the manufacturing process. Furthermore,the alloy skin layer containing Au and Pd may contain inevitableimpurities and Cu.

In the bonding wire of the present invention, the alloy skin layercontaining Au and Pd reacts with the Pd coating layer to improveadhesive strength among the alloy skin layer containing Au and Pd, thePd coating layer and the Cu alloy core material and to prevent the Pdcoating layer and the alloy skin layer containing Au and Pd from peelingat the time of wedge bonding. Accordingly, the bonding wire of thepresent invention can further improve the wedge bondability. In view ofobtaining favorable wedge bondability, a thickness of the alloy skinlayer containing Au and Pd is preferably 0.0005 μm or more, and morepreferably 0.001 μm or more, 0.002 μm or more, or 0.003 μm or more. Inview of reducing eccentricity to obtain favorable FAB shape, a thicknessof the alloy skin layer containing Au and Pd is preferably 0.050 μm orless, and more preferably 0.045 μm or less, 0.040 μm or less, 0.035 μmor less, or 0.030 μm or less. The alloy skin layer containing Au and Pdcan be formed by a method similar to that of the Pd coating layer.

In the present invention, examples of the element that provides bondingreliability in a high-temperature environment include an element ofGroup 9 of the Periodic Table of Elements (Co, Rh, Ir), an element ofGroup 10 of the Periodic Table of Elements (Ni, Pd, Pt), an element ofGroup 11 of the Periodic Table of Elements (Ag, Au and the like), anelement of Group 12 of the Periodic Table of Elements (Zn and the like),an element of Group 13 of the Periodic Table of Elements (Al, Ga, In andthe like), an element of Group 14 of the Periodic Table of Elements (Ge,Sn and the like), an element of Group 15 of the Periodic Table ofElements (P, As, Sb, Bi and the like), an element of Group 16 of thePeriodic Table of Elements (Se, Te and the like), and the like. Theseelements can be contained in the bonding wire singly or in combinationof two or more thereof.

In the present invention, it is preferable that the bonding wirecontains at least one element selected from Ni, Zn, Rh, In, Ir and Pt asthe element that provides bonding reliability in a high-temperatureenvironment. Preferably, a concentration of these elements in total is0.011 to 2% by mass relative to the entire wire.

A mold resin (an epoxy resin) as a package of a semiconductor devicecontains a silane coupling agent. The silane coupling agent has afunction of improving adhesiveness between organic matter (resin) andinorganic matter (silicon or metal) and can thereby improve adhesivenesswith a silicon substrate or metal. In a case where a higher adhesivenessis required such as a case of on-vehicle semiconductors that requirereliability at higher temperatures, a “sulfur-containing silane couplingagent” is added therein. Sulfur contained in the mold resin is liberatedwhen being used under a condition of 175° C. or more, e.g., 175° C. to200° C. When sulfur liberated at a high temperature of 175° C. or morecomes in contact with Cu, Cu drastically corrodes to produce a sulfide(Cu₂S) or an oxide (CuO). When the corrosion of Cu occurs in asemiconductor device using Cu bonding wire, a bonding reliability,especially of a ball bonded part, degrades.

The bonding reliability in a high-temperature environment (especiallythe performance in HTS at 175° C. or more) can be improved by employinga configuration where the bonding wire contains at least one elementselected from Ni, Zn, Rh, In, Ir and Pt and a concentration of the atleast one element in total is 0.011 to 2% by mass relative to the entirewire. In view of improving the bonding reliability of the ball bondedpart in a high-temperature environment (especially the performance inHTS at 175° C. or more), the concentration of the element in totalrelative to the entire wire is preferably 0.011% by mass or more, morepreferably 0.050% by mass or more, further preferably 0.070% by mass ormore, 0.090% by mass or more, 0.10% by mass or more, 0.15% by mass ormore, or 0.20% by mass or more. The at least one element selected fromNi, Zn, Rh, In, Ir and Pt may also be referred to as an “element M_(A)”in the following description.

In the present invention, it is preferable that the bonding wirecontains one or more elements selected from Ga and Ge as the elementthat provides bonding reliability in a high-temperature environment anda concentration of the elements in total is 0.011 to 1.5% by massrelative to the entire wire. The wire may contain one or more elementsselected from Ga and Ge instead of the element M_(A) or in combinationwith the element M_(A). The one or more elements selected from Ga and Gemay also be referred to as an “element M_(B)” in the followingdescription.

During formation of FAB of ball bonded part, Ga and Ge in the wirediffuse also to the Pd coating layer. It is considered that Ga and Gepresent in the Pd-concentrated layer of the Cu/Al interface in the ballbonded part enhance an effect of reducing a mutual diffusion of Cu andAl by the Pd concentrated layer, resulting in the reduction of theformation of Cu₉Al₄, which is likely to corrode in a high-temperatureand high-humidity environment. In addition, Ga and Ge contained in thewire may have the effect of directly inhibiting the formation of Cu₉Al₄.

Furthermore, when forming a ball using a Pd-coated Cu bonding wirecontaining at least one selected from Ga and Ge in certain amount andobserving a resultant FAB with a scanning electron microscope (SEM),many precipitates with a diameter of about a few tens of nanometers werefound on a surface of the FAB. From an analysis on the precipitates byenergy dispersive X-ray spectroscopy (EDS), it was revealed that Gaand/or Ge was concentrated. Although a detailed mechanism is unclear, itis considered from the above situation that these precipitates observedon the FAB become to be present at the bonding interface of the ball andthe electrode, whereby significantly improving a bonding reliability ofa ball bonded part in a high-temperature and high-humidity environmentof a temperature of 130° C. and a relative humidity of 85%.

Although it is preferable that Ga and Ge are present in the Cu alloycore material, a sufficient effect can be obtained even when they arecontained in the Pd coating layer or an alloy skin layer containing Auand Pd described below. A method of adding Ga and Ge into the Cu alloycore material is easy in terms of accurate control of concentration, andimproves wire productivity and quality stability. Further, a part of Gaand Ge is contained also in the Pd coating layer or the alloy skin layerdue to diffusion through a heat treatment or the like, whereby improvingan adhesiveness of interfaces among the layers, and thus being able tofurther improve wire productivity.

In view of obtaining favorable FAB shape and in view of reducing thehardening of the bonding wire to obtain favorable wedge bondability, theconcentration of Ga and Ge in total relative to the entire wire is 1.5%by mass or less, preferably 1.4% by mass or less, and more preferably1.3% by mass or less or 1.2% by mass or less.

In the present invention, it is preferable that the bonding wirecontains one or more elements selected from As, Te, Sn, Sb, Bi and Seand a concentration of the elements in total is 0.1 to 100 ppm by massrelative to the entire wire, provided that Sn≤10 ppm by mass, Sb≤10 ppmby mass and Bi≤1 ppm by mass. The wire may contain one or more elementsselected from As, Te, Sn, Sb, Bi and Se instead of the element M_(A)and/or M_(B) or in combination with the element M_(A) and/or M_(B). Theone or more elements selected from As, Te, Sn, Sb, Bi and Se may also bereferred to as an “element M_(C)” in the following description.

The bonding reliability of ball bonded part in a high-temperature andhigh-humidity environment required for on-vehicle devices can be furtherimproved when the bonding wire contains at least one element selectedfrom As, Te, Sn, Sb, Bi and Se and a concentration of the at least oneelement in total is 0.1 to 100 ppm by mass relative to the entire wire,provided that Sn≤10 ppm by mass, Sb≤10 ppm by mass and Bi≤1 ppm by mass.It is preferable because it can increase in particular the bondinglongevity of ball bonded part in a high-temperature and high-humidityenvironment of a temperature of 130° C. and a relative humidity of 85%required for on-vehicle devices to improve the bonding reliability. Theconcentration of the element in total relative to the entire wire ispreferably 0.1 ppm by mass or more, more preferably 0.5 ppm by mass ormore, further preferably 1 ppm by mass or more, and still furtherpreferably 1.5 ppm by mass or more, 2 ppm by mass or more, 2.5 ppm bymass or more, or 3 ppm by mass or more. On the other hand, in view ofobtaining favorable FAB shape, the concentration of the element in totalrelative to the entire wire is preferably 100 ppm by mass or less, andmore preferably 95 ppm by mass or less, 90 ppm by mass or less, 85 ppmby mass or less, or 80 ppm by mass or less. If a concentration of Sn orSb exceeds 10 ppm by mass or if a concentration of Bi exceeds 1 ppm bymass, an FAB shape becomes faulty. It is therefore preferable forfurther improving an FAB shape that Sn≤10 ppm by mass; Sb≤10 ppm bymass; and Bi≤1 ppm by mass.

It is preferable that the bonding wire of the present invention furthercontains at least one element selected from B, P, Mg, Ca and La and aconcentration of each of the elements is 1 to 200 ppm by mass relativeto the entire wire. With this configuration, there can be improved acrushed shape of a ball bonded part required for high-density mounting,that is, there can be improved a circularity of shape of a ball bondedpart. In view of reducing the hardening of ball and reducing chip damageat the time of ball bonding, the concentration of each of the elementsis preferably 200 ppm by mass or less, and more preferably 150 ppm bymass or less, 120 ppm by mass or less, 100 ppm by mass or less, 95 ppmby mass or less, 90 ppm by mass or less, 85 ppm by mass or less, or 80ppm by mass or less.

When the Pd-coated Cu bonding wire contains the element that providesbonding reliability in a high-temperature environment as in the presentinvention, if Cu is further present at an outermost surface of thebonding wire, the formation of a Cu₉Al₄ intermetallic compound in thebonded part tends to be further reduced. When the Pd-coated Cu bondingwire contains the element that provides bonding reliability in ahigh-temperature environment, if Cu is further present at an outermostsurface of the bonding wire, interaction between the elements and Cucontained in the bonding wire facilitates Pd concentration on a FABsurface during the formation of the FAB, whereby the Pd concentration ona ball bonded interface appears more remarkably. It can be estimatedthat with this phenomenon an effect of reducing mutual diffusion of Cuand Al by a Pd concentrated layer is further enhanced, a formationamount of Cu₉Al₄, which is likely to corrode through the action of Cl,is reduced, and thereby the bonding reliability of ball bonded part in ahigh-temperature and high-humidity environment can be further improved.

When Cu is present at an outermost surface of the Pd coating layer, ifthe concentration of Cu is 30 at % or more, there may be a case wherethe bonding wire is not suitable for practical use because a sulfurresistance of wire surface degrades and a service life of the bondingwire degrades. Consequently, when Cu is present at an outermost surfaceof the Pd coating layer, the concentration of Cu is preferably less than30 at %.

When Cu is present at an outermost surface of the Au skin layer, if theconcentration of Cu is 35 at % or more, there may be a case where thebonding wire is not suitable for practical use because a sulfurresistance of wire surface degrades and a service life of the bondingwire degrades. Consequently, when Cu is present at an outermost surfaceof the Au skin layer, the concentration of Cu is preferably less than 35at %.

The outermost surface refers to a region of surface of the bonding wireto be measured by an Auger electron spectroscopic apparatus withoutperforming sputtering or the like.

In the present invention, it is preferable that the Cu alloy corematerial contains a metallic element of Group 10 of the Periodic Tableof Elements in a total amount of 0.1 to 3.0% by mass and a concentrationof Cu at an outermost surface of the wire is 1 to 10 at %. With thisconfiguration, the present invention can further improve the wedgebondability to the Pd-plated lead frame or the lead frame with Auplating on Pd plating. The Cu alloy core material containing themetallic element of Group 10 of the Periodic Table of Elements in acertain amount can realize excellent ball bondability for a ball bondedpart between the bonding wire and an electrode even in a high-humidityheating condition.

It is preferable that the metallic element of Group 10 of the PeriodicTable of Elements contained in the Cu alloy core material is one or moreselected from the group consisting of Ni, Pd and Pt. In one preferableembodiment, the Cu alloy core material contains Ni as the metallicelement of Group 10 of the Periodic Table of Elements. For example, theCu alloy core material may contain Ni singly or contain Ni incombination with either or both of Pd and Pt as the metallic element ofGroup 10 of the Periodic Table of Elements. In another preferableembodiment, the Cu alloy core material contains either or both of Pd andPt as the metallic element of Group 10 of the Periodic Table ofElements.

If the total concentration of the metallic element of Group 10 of thePeriodic Table of Elements in the Cu alloy core material is 0.1% by massor more, the mutual diffusion of Cu and Al in the bonding interface canbe sufficiently controlled, and the lifetime of the bonded partincreases up to 380 hours or more even in the HAST test as a rigoroushigh-humidity heating evaluation test. As an evaluation of the bondedpart in this example, the resin is unsealed and removed after the HASTtest, and a breakage state of the bonded part is then evaluated by apull test. In view of sufficiently obtaining the effect of improvementin HAST test reliability, the total concentration of the metallicelement of Group 10 of the Periodic Table of Elements in the Cu alloycore material is 0.1% by mass or more, preferably 0.2% by mass or more,and more preferably 0.3% by mass or more, 0.4% by mass or more, 0.5% bymass or more, or 0.6% by mass or more. In view of obtaining a bondingwire favorable in initial bonding strength with the Al electrode inlow-temperature bonding and excellent in long-term reliability in theHAST test and in mass production margin of bonding to substrates such asa ball grid array (BGA) and a chip size package (CSP), tapes, and thelike and in view of reducing chip damage, the total concentration of themetallic element of Group 10 of the Periodic Table of Elements in the Cualloy core material is 3.0% by mass or less and preferably 2.5% by massor less, or 2.0% by mass or less. If the total concentration of themetallic element of Group 10 of the Periodic Table of Elements in the Cualloy core material exceeds 3.0% by mass, the ball bonding is requiredto be performed with a low load so as not to cause chip damage, and thusthere may be a case where the initial bonding strength with theelectrode decreases, resulting in deterioration in the HAST testreliability. In the bonding wire of the present invention, the totalconcentration of the metallic element of Group 10 of the Periodic Tableof Elements in the Cu alloy core material is set to the preferable rangeto further improve the HAST test reliability. There can be achieved, forexample, a bonding wire with a lifetime to the occurrence of failure inthe HAST test of more than 450 hours. This achievement may correspond to1.5 times or more enhancement of lifetime from a conventional Cu bondingwire and enables use in a harsh environment.

Examples of a method for determining a concentration of elementscontained in the Cu alloy core material from a bonding wire productinclude a method that exposes a cross-section of a bonding wire andperforms a concentration analysis of a region of the Cu alloy corematerial, and a method that performs a concentration analysis of aregion of the Cu alloy core material while trimming the bonding wirefrom its surface in a depth direction by sputtering or the like. Whenthe Cu alloy core material contains a region having a concentrationgradient of Pd, for example, line analysis may be performed on across-section of the bonding wire, and a concentration analysis may beperformed on a region that has no concentration gradient of Pd (forexample, a region in which a degree of a change in Pd concentration inthe depth direction is less than 10 mol % per 0.1 μm, or an axial centerportion of the Cu alloy core material).

The bonding wire of the present invention can remarkably improve thewedge bondability, especially peeling characteristics, to the Pd-platedlead frame, can achieve a good wedge bondability and FAB shape, and cansuppress an oxidation of wire surface to suppress a qualitydeterioration with time by using the Cu alloy core material containingthe metallic element of Group 10 of the Periodic Table of Elements in acertain amount as well as containing Cu of 1 at % or more at anoutermost surface of the wire. In view of possibly further improving thewedge bondability, in the bonding wire of the present invention, theconcentration of Cu at an outermost surface of the wire is preferably1.5 at % or more and more preferably 2 at % or more, 2.5 at % or more,or 3 at % or more. Although an upper limit of the concentration of Cu atan outermost surface of the wire has been noted above, in the bondingwire of the present invention including the Cu alloy core materialcontaining the metallic element of Group 10 of the Periodic Table ofElements in a certain amount, the concentration of Cu at an outermostsurface of the wire is preferably 10 at % or less, and more preferably9.5 at % or less or 9 at % or less, in view of achieving favorable wedgebondability and FAB shape and in view of suppressing the oxidation ofwire surface to suppress a quality deterioration with time.

For a concentration analysis of the Pd coating layer and the alloy skinlayer containing Au and Pd, a method of performing analysis whiletrimming the bonding wire from its surface in the depth direction bysputtering or the like, or a method of exposing a cross-section of thewire and performing a line analysis, a point analysis, or the likethereon is effective. For an analyzer used for such concentrationanalysis, an Auger electron spectroscopic apparatus installed in ascanning electron microscope or a transmission electron microscope, anenergy dispersive X-ray analyzer, and an electron probe micro analyzer,etc., can be applied. As a method for exposing a cross-section of wire,a mechanical polishing, an ion etching, etc., can be applied. For amicroanalysis of Ni, Zn, Rh, In, Ir and Pt in the bonding wire, asolution obtained by dissolving the bonding wire with a strong acid isanalyzed using an ICP emission spectrometer or an ICP mass spectrometer,thereby enabling detection as the concentrations of elements containedin the entire bonding wire.

(Method of Manufacture)

Next, there will be described a method for manufacturing the bondingwire according to the embodiment of the present invention. The bondingwire is obtained by manufacturing a Cu alloy used for a core material,working it into a thin wire, forming a Pd coating layer and an Au layer,and performing heat treatment. After forming the Pd coating layer andthe Au layer, another wire drawing and heat treatment may be performed.There will be described in detail a method for manufacturing the Cualloy core material, a method for forming the Pd coating layer and analloy skin layer containing Au and Pd, and a method of heat treatment.

The Cu core alloy used for a core material is obtained by melting Cu asa raw material and additive elements together and solidifying them. Anarc heating furnace, a high-frequency heating furnace, a resistanceheating furnace, or the like can be used for the melting. In order toprevent gases such as O₂ and H₂ being mixed therein from air, themelting is preferably performed in a vacuum atmosphere or an inertatmosphere such as Ar or N₂.

Examples of a method for forming the Pd coating layer and the Au layeron a surface of the Cu alloy core material include a plating method, avapor deposition method, and a melting method. Both of an electroplatingmethod and an electroless plating method can be used as the platingmethod. The electroplating called a strike plating or a flash plating ishigh in plating speed and is favorable in adhesiveness with a substrate.A solution used for the electroless plating is classified into asubstitutional type and a reduction type. Although performing thesubstitutional type plating alone is sufficient for a smaller thickness,it is effective for a larger thickness to perform the reduction typeplating after the substitutional type plating in a step-by-step manner.

For a vapor deposition method, there can be used a physical adsorptionsuch as a sputtering method, an ion plating method and a vacuum vapordeposition, and a chemical adsorption such as plasma CVD. They are alldry processes, and are free from the necessity of cleaning after formingthe Pd coating layer and the Au layer and from any concern about surfacecontamination and the like during cleaning.

When heat treatment is performed after forming the Pd coating layer andthe Au layer, Pd in the Pd coating layer diffuses into the Au layer toform the alloy skin layer containing Au and Pd. Instead of forming thealloy skin layer containing Au and Pd through the heat treatment afterforming the Au layer, the alloy skin layer containing Au and Pd may bedeposited from the beginning.

For a formation of the Pd coating layer and the alloy skin layercontaining Au and Pd, both a method of forming them after performingwire drawing to a final wire diameter and a method of forming them on aCu alloy core material of large diameter and then performing wiredrawing several times until obtaining a target wire diameter areeffective. In the former in which the Pd coating layer and the alloyskin layer containing Au and Pd are formed at the final wire diameter,manufacture, quality control, and the like are simple. In the latter inwhich the wire drawing is performed in combination with the formed Pdcoating layer and alloy skin layer containing Au and Pd, there is theadvantage that adhesiveness with the Cu alloy core material improves.Specific examples of the respective formation methods include a methodof forming the Pd coating layer and the alloy skin layer containing Auand Pd on a Cu alloy core material with a final diameter whilesuccessively sweeping the wire through an electroplating solution and amethod of forming the Pd coating layer and the alloy skin layercontaining by immersing a Cu alloy core material of large diameter intoan electro or electroless plating solution and then drawing the wire toachieve a final diameter of wire.

After forming the Pd coating layer and the alloy skin layer containingAu and Pd, heat treatment may be performed. By performing the heattreatment, diffusion of atoms occurs among the alloy skin layercontaining Au and Pd, the Pd coating layer and the Cu alloy corematerial, which improves adhesive strength therebetween and is effectivein that the alloy skin layer containing Au and Pd and the Pd coatinglayer are prevented from peeling during working, and thus, improvingproductivity. In order to prevent O₂ being mixed therein from air, it ispreferable to perform the heat treatment in a vacuum atmosphere or aninert atmosphere such as Ar or N₂.

As described above, when a condition of diffusion heat treatment orannealing heat treatment performed on the bonding wire are adjusted, Cuof the core material diffuses through the Pd coating layer and the skinalloy layer containing Au and Pd by grain boundary diffusion, intragraindiffusion, or the like, enabling Cu to reach an outermost surface of thebonding wire and allows Cu to be present at an outermost surface. For aheat treatment of allowing Cu to be present at an outermost surface,there can be used a heat treatment for forming the alloy skin layercontaining Au and Pd as described above. When performing the heattreatment for forming the alloy skin layer, the temperature and time forheat treatment can be selected to allow Cu to be present at an outermostsurface, or allow Cu to be not present at an outermost surface.Furthermore, it is also able to adjust a concentration of Cu at anoutermost surface to a certain range, e.g., a range of 1 to 50 at %.Alternatively, Cu may be diffused to an outermost surface by heattreatment performed at other than the formation of the alloy skin layer.

As described above, as for addition of the element that provides bondingreliability in a high-temperature environment into the bonding wire, theeffect of the invention can be exhibited by either of the method ofadding these elements into the Cu core material or the method of addingthese elements therein by depositing these elements onto the Cu corematerial or the wire surface. The same shall apply for B, P, Mg, Ca andLa.

The simplest method for adding the components is a method of adding themto starting materials of the Cu alloy core material. For example,high-purity copper and raw materials of the above component element areweighed as starting raw materials and are then heated and melted in ahigh vacuum or in an inert atmosphere such as nitrogen and argon toproduce an ingot in which the components have been added at theconcentration of the intended range, thus obtaining the startingmaterials containing the component elements at the intendedconcentrations. Consequently, in a preferable embodiment, the Cu alloycore material of the bonding wire of the present invention contains atleast one element selected from Ni, Zn, Rh, In, Ir and Pt so that aconcentration of the elements in total relative to the entire wire willbe 0.011 to 2% by mass. The preferable numerical range of the totalconcentration is as described above. In another preferable embodiment,the Cu alloy core material of the bonding wire of the present inventioncontains one or more elements selected from Ga and Ge so that aconcentration of the elements in total relative to the entire wire willbe 0.011 to 1.5% by mass. The preferable numerical range of the totalconcentration is as described above. In another preferable embodiment,the Cu alloy core material of the bonding wire of the present inventioncontains at least one element selected from As, Te, Sn, Sb, Bi and Se sothat a concentration of the elements will be 0.1 to 100 ppm by mass, andSn 10 ppm by mass; Sb≤10 ppm by mass; and Bi≤1 ppm by mass. Thepreferable numerical range of the concentration is as described above.In a preferable embodiment, the purity of Cu of the Cu alloy corematerial is 3N or less (preferably 2N or less). In a conventionalPd-coated Cu bonding wire, in view of bondability, a Cu core materialwith high purity (4N or more) is used, and there is a tendency to avoidthe use of a Cu core material with low purity. The bonding wire of thepresent invention containing the specific elements has achieved thebonding reliability of the ball bonded part in a high-temperature andhigh-humidity environment required for on-vehicle devices, especiallypreferably when using the Cu alloy core material of low Cu purity asdescribed above. In another preferable embodiment, the Cu alloy corematerial of the bonding wire of the present invention contains at leastone element selected from B, P, Mg, Ca and La so that a concentration ofeach of the elements relative to the entire wire will be 1 to 200 ppm bymass. The preferable numerical range of the concentration is asdescribed above. In another preferable embodiment, the Cu alloy corematerial of the bonding wire of the present invention contains ametallic element of Group 10 of the Periodic Table of Elements so that aconcentration of the elements in total will be 0.1 to 3.0% by mass. Thepreferable numerical range of the concentration is as described above.

The above components can also be contained by depositing them on asurface of wire during a manufacturing process of wire. In this case,the deposition may be incorporated into any part of the manufacturingprocess of wire and may be repeated several times. The deposition mayalso be incorporated into a plurality of processes. The components maybe added to a Cu surface before Pd coating, or may be added to a Pdsurface after Pd coating, or may be added to an Au surface after Aucoating, or may be incorporated into each coating process. A method ofdeposition can be selected from (1) application of an aqueous solution,followed by drying and heat treatment, (2) plating (wet), and (3) vapordeposition (dry).

When employing the method of application of an aqueous solution,followed by drying and heat treatment, first, an aqueous solution of anappropriate concentration is prepared with a water-soluble compoundcontaining the component elements. The components can be thusincorporated into the wire material. The preparation may be incorporatedinto any part of the manufacturing process of wire and may be repeatedseveral times. The preparation may be incorporated into a plurality ofprocesses. The components may be added to a Cu surface before Pdcoating, or may be added to a Pd surface after Pd coating, or may beadded to an Au surface after Au coating, or may be incorporated intoeach coating process.

When plating (wet) is used, plating can be either of electroplating orelectroless plating. In electroplating, plating called flash plating,which is high in plating speed and favorable in adhesiveness with asubstrate, can also be used in addition to normal electroplating. Asolution for use in electroless plating is classified into asubstitutional type and a reduction type. The substitutional typeplating is generally used for a smaller thickness, whereas the reductiontype is used for a larger thickness. Either of them can be used and maybe selected depending on a concentration desired to be added, and aplating solution concentration and a time may be adjusted. Bothelectroplating and electroless plating may be incorporated into any partof the manufacturing process of wire and may be repeated several times.Both electroplating and electroless plating may be incorporated into aplurality of processes. The components may be added to a Cu surfacebefore Pd coating, or may be added to a Pd surface after Pd coating, ormay be added to an Au surface after Au coating, or may be incorporatedinto each coating process.

The vapor deposition (dry) includes sputtering, ion plating, vacuumdeposition, plasma CVD, and the like. It has advantages in that it isdry process and eliminates pretreatment and posttreatment, giving noconcern about contamination. Although vapor deposition generally has aproblem that an addition speed of a target element is slow, it is one ofappropriate methods in light of the object of the present inventionbecause an addition amount of the above component elements is relativelylow.

The vapor deposition may be incorporated into any part of themanufacturing process of wire or may be repeated several times. Thevapor deposition may be incorporated into a plurality of processes. Thecomponents may be added to a Cu surface before Pd coating, or may beadded to a Pd surface after Pd coating, or may be added to an Au surfaceafter Au coating, or may be incorporated into each coating processes.

There will be described a method for manufacture by which, a crystalorientation <100> angled at 15 degrees or less to a wire longitudinaldirection among crystal orientations in the wire longitudinal directionhas a proportion of 30% or more when measuring crystal orientations on across-section of the core material in a direction perpendicular to awire axis of the bonding wire, and an average crystal grain size in thecross-section of the core material in the direction perpendicular to thewire axis of the bonding wire is 0.9 to 1.5 μm.

When the bonding wire contains the element that provides bondingreliability in a high-temperature environment in the Cu alloy corematerial, the material strength (hardness) of the wire increases.Consequently, when performing wire drawing on the bonding wire with a Cucore wire, an area reduction rate at the time of wire drawing was as lowas 5 to 8%. In heat treatment after wire drawing, the hardness is stillhigh, and heat treatment was performed at a temperature of 600° C. ormore in order to perform softening to a level capable of being used asthe bonding wire. Owing to the heat treatment of high temperature, the<100> orientation proportion in the wire longitudinal direction was lessthan 30%, and at the same time, the average crystal grain size in thecross-section of the core material was more than 1.5 μm, and thestrength ratio was more than 1.6. When decreasing heat treatmenttemperature in an attempt to reduce the strength ratio, the averagecrystal grain size in the cross-section of the core material was lessthan 0.9 μm, the strength ratio was less than 1.1, and the wedgebondability was inferior.

In contrast, the present invention, at the time of wire drawing using adie, sets the area reduction rate to 10% or more in half or more diesamong all dies and sets the heat treatment temperature at the heattreatment after wire drawing to a low temperature of 500° C. or less.Consequently, when measuring crystal orientations on a cross-section ofthe core material in the direction perpendicular to the wire axis of thebonding wire, the orientation proportion of the crystal orientation<100> angled at 15 degrees or less to a wire longitudinal directionamong the crystal orientations in the wire longitudinal direction couldbe 30% or more, and the average crystal grain size in the cross-sectionof the core material in the direction perpendicular to the wire axis ofthe bonding wire could be 0.9 to 1.5 μm. Owing to synergy of using thelatest technique of wire drawing; as for a lubricant, designing aconcentration of non-ionic surfactant contained in the lubricant athigher than a conventional one; as for a die shape, designing anapproach angle of the die gentler than a conventional one; setting atemperature of cooling water of the die to lower than a conventionalone; and the like, a wire drawing with an area reduction rate of 10% ormore was enabled despite the hardening caused by the Cu alloy corematerial containing the components such as Ni in a total amount of 0.03%by mass or more.

When measuring crystal orientations on a cross-section of wire, anelectron backscattered diffraction (EBSD) method is preferably used. TheEBSD method is characterized in that it can observe crystal orientationson an observation surface and can graphically show an angle differenceof the crystal orientations between adjacent measurement points.Further, the EBSD method can relatively easily observe the crystalorientations with high accuracy, even for a thin wire like the bondingwire. As for measurement of grain size, it can be determined by usinganalysis software installed in an apparatus for measurement results byEBSD. The crystal grain size prescribed in the present invention isobtained by performing an arithmetic mean on an equivalent diameter ofcrystal grains contained in a measurement area (the diameter of a circleequivalent to an area of a crystal grain; a circle-equivalent diameter).

The present invention is not limited to the above embodiments, andappropriate alterations can be made within the scope of the spirit ofthe present invention.

EXAMPLES

The bonding wires according to embodiments of the present invention willbe described in detail below with reference to examples.

Working Examples 1 to 59 and Comparative Examples 1 to 16

(Manufacture of Sample)

First, the following describes a method for manufacturing a sample. ForCu as a raw material of a core material, Cu with a purity of 99.99% bymass or more and containing inevitable impurities as the remainder wasused. For Au, Pd, Ni, Zn, Rh, In, Ir and Pt, the ones with a purity of99% by mass or more and containing inevitable impurities as theremainder were used. Additive elements to the core material (Ni, Zn, Rh,In, Ir and Pt) are mixed so that the wire or the core material will havea desired composition. Regarding the addition of Ni, Zn, Rh, In, Ir andPt, they can be mixed singly. Alternatively, they may be mixed so as tobe a desired amount using a Cu master alloy containing the additiveelements manufactured in advance if the element has a high melting pointas a single body or if the element is added in an infinitesimal amount.Working examples 27 to 47 further contain one or more of Ga, Ge, As, Te,Sn, Sb, Bi, Se, B, P, Mg, Ca and La.

The Cu alloy as the core material was manufactured to give a wirediameter of a few millimeters by continuous casting. The obtained alloywith a diameter of a few millimeters was drawn to manufacture a wirewith a diameter of 0.3 to 1.4 mm. A commercially available lubricant wasused for the wire drawing, and a wire drawing speed was 20 to 150 m/min.In order to remove an oxide film on a surface of wire, picklingtreatment with hydrochloric acid or the like was performed, and a Pdcoating layer was formed by 1 to 15 μm so as to cover the entire surfaceof the Cu alloy as the core material. Furthermore, for some wires, analloy skin layer containing Au and Pd was formed by 0.05 to 1.5 μm onthe Pd coating layer. For the formation of the Pd coating layer and thealloy skin layer containing Au and Pd, electroplating was used. Acommercially available semiconductor plating solution was used for aplating solution. Thereafter, wire drawing was performed mainly usingdies with an area reduction rate of 10 to 21%, and furthermore, one tothree pieces of heat treatment were performed at 200 to 500° C. duringthe wire drawing to perform working to a diameter of 20 μm. Afterworking, heat treatment was performed so that breaking elongation wouldfinally be about 5 to 15%. A method of heat treatment was performedwhile successively sweeping the wire and was carried out while flowingan N₂ or Ar gas. A wire feeding speed was 10 to 90 m/min, a heattreatment temperature was 350 to 500° C., and a heat treatment time was1 to 10 seconds.

(Method of Evaluation)

The contents of Ni, Zn, Rh, In, Ir, Pt, Ga, Ge, As, Te, Sn, Sb, Bi, Se,B, P, Mg, Ca and La in the wire were analyzed as the concentrations ofthe elements contained in the entire bonding wire using an ICP emissionspectrometer.

For the concentration analysis of the Pd coating layer and the alloyskin layer containing Au and Pd, Auger electron spectrometry wasperformed while trimming the bonding wire from its surface in the depthdirection by sputtering or the like. From an obtained concentrationprofile in the depth direction, a thickness of the Pd coating layer, amaximum concentration of Pd in the Pd coating layer and a thickness ofthe alloy skin layer containing Au and Pd were determined.

The orientation proportion of the crystal orientation <100> angled at 15degrees or less to the wire longitudinal direction among the crystalorientations in the wire longitudinal direction in the cross-section ofthe core material in the direction perpendicular to the wire axis of thebonding wire was calculated by observing crystal orientations of anobservation surface (that is, the cross-section of the core material inthe direction perpendicular to the wire axis) by EBSD. For the analysisof EBSD measurement data, exclusive software (OIM analysis manufacturedby TSL Solutions, for example) was used. The average crystal grain sizein the cross-section of the core material in the direction perpendicularto the wire axis was calculated by observing the crystal orientations onthe observation surface by EBSD. For the analysis of EBSD measurementdata, exclusive software (OIM analysis manufactured by TSL Solutions,for example) was used. The crystal grain size was obtained by performingan arithmetic mean on an equivalent diameter of crystal grains containedin a measurement area (the diameter of a circle equivalent to an area ofa crystal grain; a circle-equivalent diameter).

The 0.2% offset yield strength and the ultimate strength were evaluatedby performing a tensile test with an inter-mark distance of 100 mm. Auniversal material test machine Type 5542 manufactured by Instron wasused for a tensile test apparatus. The 0.2% offset yield strength wascalculated using exclusive software installed in the apparatus. A loadat the time of breaking was determined to be the ultimate strength. Thestrength ratio was calculated from the following Equation (1)Strength ratio=ultimate strength/0.2% offset yield strength.  (1)

The evaluation of the wedge bondability in the wire bonded part wasdetermined by performing 1,000 pieces of bonding on wedge bonding partsof a BGA substrate and by the occurrence frequency of peeling of thebonded parts. The used BGA substrate was plated with Ni and Au. In thisevaluation, assuming bonding conditions more rigorous than normal, astage temperature was set to 150° C., which was lower than a general settemperature range. In the evaluation, a case in which 11 or morefailures occurred was determined to be problematic to be marked with asymbol of “cross,” a case of 6 to 10 failures was determined to bepracticable but somewhat problematic to be marked with a symbol of“triangle,” a case of 1 to 5 failures was determined to be no problem tobe marked with a symbol of “circle,” and a case in which no failureoccurred was determined to be excellent to be marked with a symbol of“double circle” in the column “wedge bondability” in Tables 1 to 4.

The bonding reliability of the ball bonded part in a high-temperatureand high humidity environment or a high-temperature environment wasdetermined by manufacturing a sample for bonding reliability evaluation,performing HTS evaluation, and evaluating the bonding longevity of theball bonded part. The sample for bonding reliability evaluation wasmanufactured by performing ball bonding onto an electrode, which hasbeen formed by forming an alloy of Al-1.0% Si-0.5% Cu as a film with athickness of 0.8 μm on a Si substrate on a general metallic frame, usinga commercially available wire bonder and sealing it with a commerciallyavailable epoxy resin. A ball was formed while flowing an N₂ 5% H₂ gasat a flow rate of 0.4 to 0.6 L/min, and its size was within the range ofa diameter of 33 to 34 μm.

For the HTS evaluation, the manufactured sample for bonding reliabilityevaluation was exposed to a high-temperature environment with atemperature of 200° C. using a high-temperature thermostatic device. Ashear test on the ball bonded part was performed every 500 hours, and atime until a value of shear strength became half of the initial shearstrength was determined to be the bonding longevity of the ball bondedpart. The shear test after the high-temperature and high-humidity testwas performed after removing the resin by acid treatment and exposingthe ball bonded part.

A tester manufactured by DAGE was used for a shear tester for the HTSevaluation. An average value of measurement values of 10 ball bondedparts randomly selected was used for the value of the shear strength. Inthe above evaluation, the bonding longevity being less than 500 hourswas determined to be impracticable to be marked with a symbol of“cross,” being 500 hours or more and less than 1,000 hours wasdetermined to be practicable but desired to be improved to be markedwith a symbol of “triangle,” being 1,000 hours or more and less than3,000 hours was determined to be practically no problem to be markedwith a symbol of “circle,” and being 3,000 hours or more was determinedto be especially excellent to be marked with a symbol of “double circle”in the column “HTS” in Tables 1 to 4.

For the evaluation of ball formability (FAB shape), a ball beforeperforming bonding was collected and observed, and the presence orabsence of voids on a surface of the ball and the presence or absence ofdeformation of the ball, which is primarily a perfect sphere, weredetermined. The occurrence of any of the above was determined to befaulty. The formation of the ball was performed while blowing an N₂ gasat a flow rate of 0.5 L/min in order to reduce oxidation in a meltingprocess. The size of the ball was 34 μm. For one condition, 50 ballswere observed. A SEM was used for the observation. In the evaluation ofthe ball formability, a case in which five or more failures occurred wasdetermined to be problematic to be marked with a symbol of “cross,” acase of three or four failures was determined to be practicable butsomewhat problematic to be marked with a symbol of “triangle,” a case ofone or two failures was determined to be no problem to be marked with asymbol of “circle,” and a case in which no failure occurred wasdetermined to be excellent to be marked with a symbol of “double circle”in the column “FAB shape” in Tables 1 to 4.

The bonding longevity of the ball bonded part in the high-temperatureand high-humidity environment with a temperature of 130° C. and arelative humidity of 85% can be evaluated by the following HASTevaluation. For the HAST evaluation, the manufactured sample for bondingreliability evaluation was exposed to a high-temperature andhigh-humidity environment with a temperature of 130° C. and a relativehumidity of 85% using an unsaturated type pressure cooker tester and wasbiased with 5 V. A shear test on the ball bonded part was performedevery 48 hours, and a time until a value of shear strength became halfof the initial shear strength was determined to be the bonding longevityof the ball bonded part. The shear test after the high-temperature andhigh-humidity test was performed after removing the resin by acidtreatment and exposing the ball bonded part.

A tester manufactured by DAGE was used for a shear tester for the HASTevaluation. An average value of measurement values of 10 ball bondedparts randomly selected was used for the value of the shear strength. Inthe above evaluation, the bonding longevity being less than 144 hourswas determined to be impracticable to be marked with a symbol of“cross,” being 144 hours or more and less than 288 hours was determinedto be practically no problem to be marked with a symbol of “circle,”being 288 hours or more and less than 384 hours was determined to beexcellent to be marked with a symbol of “double circle,” and being 384hours or more was determined to be especially excellent to be markedwith a symbol of “a pair of double circles” in the column “HAST” inTables 1 to 4.

The evaluation of a crushed shape of the ball bonded part was determinedby observing the ball bonded part from immediately above after bondingand evaluating by its circularity. For a bonding counterpart, anelectrode in which an Al-0.5% Cu alloy was formed as a film with athickness of 1.0 μm on a Si substrate was used. The observation wasperformed using an optical microscope, and 200 sites were observed forone condition. Being elliptic with large deviation from a perfect circleand being anisotropic in deformation were determined to be faulty in thecrushed shape of the ball bonded part. In the above evaluation, a casein which one to three failures was determined to be no problem to bemarked with a symbol of “circle,” and a case in which a favorableperfect circle was obtained for all was determined to be especiallyexcellent to be marked with a symbol of “double circle” in the column“crushed shape” in Tables 1 to 4.

TABLE 1 Crystal structure Mechanical Thick- <100> characteristics nessPro- 0.2% Coating layer of portion Average Offset Additive element (% bymass) Pd alloy of crystal Ultimate yield Strength M_(A) Thick- maximumskin wire C grain strength strength ratio Wire quality M_(A) in nessconcentration layer section size {circle around (1)} {circle around (2)}{circle around (1)}/{circle around (2)} Wedge FAB Crushed No. Ni Pt ZnRh In Ir total Other (μm) (at %) (μm) (%) (μm) (mN/μm²) — bondabilityHTS shape HAST shape Working 1 0.7 0.7 0.015 97 — 92 1.1 0.19 0.16 1.19⊚ ⊚ ◯ ◯ ◯ Example 2 1.2 1.2 0.050 100 — 72 0.9 0.22 0.17 1.29 ⊚ ⊚ ⊚ ◯ ◯3 1.0 1.0 0.100 100 — 71 1.0 0.24 0.16 1.50 ◯ ⊚ ⊚ ◯ ◯ 4 0.5 0.5 0.150100 — 72 1.1 0.29 0.24 1.21 ⊚ ⊚ ◯ ◯ ◯ 5 0.1 0.1 0.015 98 — 75 1.2 0.300.22 1.36 ⊚ ⊚ ◯ ◯ ◯ 6 0.03 0.03 0.050 100 — 63 1.3 0.31 0.20 1.55 ◯ ⊚ ⊚◯ ◯ 7 1.1 0.3 1.4 0.100 100 — 75 1.0 0.33 0.28 1.18 ⊚ ⊚ ⊚ ◯ ◯ 8 1.2 0.82.0 0.150 100 — 65 0.9 0.34 0.27 1.26 ⊚ ⊚ ◯ ◯ ◯ 9 0.1 0.7 0.8 0.015 98 —51 1.2 0.35 0.22 1.59 ◯ ⊚ ◯ ◯ ◯ 10 0.6 0.1 0.05 0.75 0.100 100 — 97 1.20.33 0.30 1.10 ⊚ ⊚ ⊚ ◯ ◯ 11 0.8 0.8 0.3 1.9 0.150 100 — 80 1.1 0.34 0.281.21 ⊚ ⊚ ◯ ◯ ◯ 12 0.05 0.05 0.05 0.15 0.015 99 — 70 1.2 0.35 0.22 1.59 ◯⊚ ◯ ◯ ◯ 13 0.3 1.0 1.0 1.4 0.015 97 — 54 1.0 0.35 0.23 1.52 ⊚ ⊚ ◯ ◯ ◯ 140.5 0.5 0.015 98 0.0005 91 1.1 0.20 0.18 1.11 ⊚ ⊚ ◯ ◯ ◯ 15 1.2 1.2 0.050100 0.0010 70 0.9 0.21 0.17 1.24 ⊚ ⊚ ⊚ ◯ ◯ 16 0.7 0.7 0.100 100 0.010069 1.1 0.22 0.15 1.47 ⊚ ⊚ ⊚ ◯ ◯ 17 0.3 0.3 0.150 100 0.0500 70 1.2 0.280.24 1.17 ⊚ ⊚ ◯ ◯ ◯ 18 0.1 0.1 0.015 98 0.0005 76 1.2 0.29 0.22 1.32 ⊚ ⊚◯ ◯ ◯ 19 0.05 0.05 0.050 100 0.0010 64 1.3 0.30 0.19 1.58 ⊚ ⊚ ⊚ ◯ ◯ 200.5 0.3 0.8 0.100 100 0.0100 74 1.1 0.33 0.28 1.18 ⊚ ⊚ ⊚ ◯ ◯ 21 1.2 0.11.3 0.150 100 0.0500 64 1.2 0.34 0.26 1.31 ⊚ ⊚ ◯ ◯ ◯ 22 0.01 0.7 0.710.015 99 0.0005 50 1.1 0.35 0.23 1.52 ◯ ⊚ ◯ ◯ ◯ 23 0.6 0.1 0.05 0.750.050 100 0.0010 98 1.0 0.30 0.20 1.50 ⊚ ⊚ ⊚ ◯ ◯ 24 0.8 0.8 0.3 1.90.100 100 0.0100 85 0.9 0.33 0.29 1.14 ⊚ ⊚ ⊚ ◯ ◯ 25 0.05 0.05 0.05 0.150.150 100 0.0500 74 1.3 0.34 0.25 1.36 ⊚ ⊚ ◯ ◯ ◯ 26 0.3 1.0 0.1 1.40.015 97 0.0100 51 0.9 0.35 0.25 1.40 ⊚ ⊚ ◯ ◯ ◯

TABLE 2 Thick- Mechanical characteristics ness Crystal structure 0.2%Coating layer of <100> Average Offset Additive element (% by mass) Pdalloy Proportion crystal Ultimate yield Strength M_(A) Thick- maximumskin of wire C grain strength strength ratio Wire quality M_(A) in nessconcentration layer section size {circle around (1)} {circle around (2)}{circle around (1)}/{circle around (2)} Wedge FAB Crushed No. Ni Pt ZnRh In Ir total other (μm) (at %) (μm) (%) (μm) (mN/μm²) — bondabilityHST shape HAST shape Working 27 0.7 0.7 Gn: 0.007 0.100 100 — 88 0.90.22 0.18 1.22 ⊚ ⊚ ⊚ ⊚ ◯ Example 28 1.1 1.1 Ge: 0.008 0.050 100 — 75 1.00.25 0.17 1.47 ⊚ ⊚ ⊚ ⊚ ◯ 29 0.7 0.7 As: 0.003 0.050 100 — 72 1.0 0.300.21 1.43 ⊚ ⊚ ⊚ ⊚ ◯ 30 1.2 1.2 Te: 0.001 0.150 100 — 67 1.2 0.31 0.241.29 ⊚ ⊚ ◯ ⊚ ◯ 31 0.5 0.5 Sn: 0.0007 0.015 96 — 66 1.0 0.29 0.22 1.32 ⊚⊚ ◯ ⊚ ◯ 32 0.05 0.05 Sb: 0.0008 0.050 100 — 74 1.1 0.35 0.29 1.21 ⊚ ⊚ ⊚⊚ ◯ 33 1.0 1.0 Bi: 0.00008 0.100 100 — 80 1.1 0.31 0.22 1.41 ⊚ ⊚ ⊚ ⊚ ◯34 0.8 0.8 Se: 0.0001 0.100 100 — 92 0.9 0.27 0.19 1.42 ⊚ ⊚ ⊚ ⊚ ◯ 350.05 0.05 Gn: 0.003 0.100 100 — 72 1.2 0.30 0.19 1.58 ◯ ⊚ ⊚ ⊚ ◯ Te:0.0008 36 0.08 0.08 Gn: 0.003 0.150 100 0.0050 55 1.3 0.33 0.25 1.32 ⊚ ⊚◯ ⊚ ◯ Sb: 0.0007 37 0.1 0.1 As: 0.001 0.150 100 0.0100 82 1.1 0.32 0.251.28 ⊚ ⊚ ◯ ⊚ ◯ Se: 0.001 38 0.08 0.08 B: 0.0008 0.050 100 — 74 1.1 0.340.23 1.48 ⊚ ⊚ ⊚ ◯ ⊚ 39 1.2 1.2 P: 0.004 0.050 100 — 77 1.2 0.29 0.201.45 ⊚ ⊚ ⊚ ◯ ⊚ 40 0.05 0.05 Mg: 0.005 0.100 100 — 91 1.0 0.33 0.28 1.18⊚ ⊚ ⊚ ◯ ⊚ 41 0.5 0.5 Ca: 0.003 0.015 95 — 68 1.0 0.23 0.19 1.21 ⊚ ⊚ ◯ ◯⊚ 42 0.1 0.1 La: 0.003 0.100 100 0.0100 91 0.9 0.26 0.21 1.24 ⊚ ⊚ ⊚ ◯ ⊚43 0.05 0.05 P: 0.006 0.050 100 0.0050 68 1.1 0.29 0.19 1.53 ◯ ⊚ ⊚ ◯ ⊚B: 0.0008 44 0.6 0.6 P: 0.003 0.015 100 0.0100 57 1.3 0.33 0.24 1.38 ⊚ ⊚◯ ◯ ⊚ Ca: 0.001 45 0.5 0.5 B: 0.015 0.100 100 0.0100 90 0.9 0.25 0.211.19 ⊚ ⊚ ⊚ ◯ ⊚ 46 0.5 0.5 P: 0.02 0.050 100 0.0050 67 1.1 0.28 0.19 1.47⊚ ⊚ ⊚ ◯ ⊚ 47 0.5 0.5 La: 0.018 0.015 100 0.0100 56 1.3 0.33 0.24 1.38 ⊚⊚ ◯ ◯ ⊚ 48 0.011 0.011 0.015 98 — 75 1.0 0.21 0.18 1.17 ⊚ ◯ ◯ ◯ ◯ 490.011 0.011 0.050 100 — 72 1.0 0.19 0.16 1.19 ⊚ ◯ ⊚ ◯ ◯ 50 0.011 0.0110.100 100 — 67 1.2 0.23 0.19 1.21 ⊚ ◯ ⊚ ◯ ◯ 51 0.011 0.011 0.150 100 —66 1.0 0.22 0.18 1.22 ⊚ ◯ ◯ ◯ ◯ 52 0.011 0.011 0.050 100 — 74 1.1 0.210.18 1.17 ⊚ ◯ ⊚ ◯ ◯ 53 0.011 0.011 0.100 100 — 80 0.9 0.23 0.2 1.15 ⊚ ◯⊚ ◯ ◯

TABLE 3 Thick- ness Coating layer of Additive element (% by mass) Pdalloy M_(A) Thick- maximum skin M_(A) in ness concentration layer No. NiPt Zn Rh In Ir total other (μm) (at %) (μm) Working 54 0.02 0.02 0.01597 — Example 55 0.02 0.02 0.05 100 — 56 0.02 0.02 0.1 100 — 57 0.02 0.020.15 100 — 58 0.02 0.02 0.05 100 — 59 0.02 0.02 0.1 100 — Mechanicalcharacteristics Crystal structure 0.2% <100> Average Offset Proportioncrystal Ultimate yield Strength of wire C grain strength strength ratioWire quality section size {circle around (1)} {circle around (2)}{circle around (1)}/{circle around (2)} Wedge FAB Crushed No. (%) (μm)(mN/μm²) — bondability HTS shape HAST shape Working 54 30 1 0.31 0.241.29 ⊚ ◯ ◯ ◯ ◯ Example 55 41 1 0.33 0.22 1.50 ⊚ ◯ ⊚ ◯ ◯ 56 49 1.2 0.280.19 1.47 ⊚ ◯ ⊚ ◯ ◯ 57 52 1.3 0.32 0.27 1.19 ⊚ ◯ ◯ ◯ ◯ 58 60 1.4 0.220.18 1.22 ⊚ ◯ ⊚ ◯ ◯ 59 74 1.5 0.25 0.20 1.25 ⊚ ◯ ⊚ ◯ ◯

TABLE 4 Additive element Ni Pd Pt Zn Rh In Ir Gn Ge (% by mass) As Te SnSb Bi Se No. (Amount in core material for Pd (% by mass)) (ppm by mass)Com- 1 0.7 parative 2 1.2 0.8 Example 3 0.6 0.1 0.05 4 0.03 5 0.1 0.7 60.8 0.8 0.3 7 0.7 1.2 8 1.1 0.3 9 0.05 0.05 0.05 10 0.05 1.2 0.9 11 11.1 1.1 12 0.05 1.3 1.1 13 1 1.1 1.2 0.8 14 0.05 0.05 1.1 0.9 1.2 15 16Thick- Mechanical characteristics ness Crystal structure 0.2% Pd coatinglayer of <100> Average Offset Pd alloy Proportion crystal Ultimate yieldStrength Thick- maximum skin of wire C grain strength strength ratioWire quality ness concentration layer section size {circle around (1)}{circle around (2)} {circle around (1)}/{circle around (2)} Wedge FABCrushed No. (μm) (at %) (μm) (%) (μm) (mN/μm²) — bondability HTS shapeHAST shape Com- 1 0.015 98 — 50 0.8 0.35 0.32 1.09 X ⊚ ◯ ◯ ◯ parative 20.150 100 — 29 1.7 0.29 0.16 1.81 X ⊚ ◯ ◯ ◯ Example 3 0.100 100 — 51 0.70.28 0.26 1.08 X ⊚ ⊚ ◯ ◯ 4 0.050 100 — 25 0.9 0.21 0.12 1.75 X ⊚ ⊚ ◯ ◯ 50.015 96 — 20 1.1 0.30 0.17 1.76 X ⊚ ◯ ◯ ◯ 6 0.150 100 — 21 1.6 0.350.19 1.84 X ⊚ ◯ ◯ ◯ 7 0.050 100 — 22 1.0 0.21 0.12 1.75 X ⊚ ⊚ ◯ ◯ 80.100 100 — 25 1.6 0.30 0.18 1.67 Δ ⊚ ⊚ ◯ ◯ 9 0.015 97 — 28 1.8 0.340.20 1.70 Δ ⊚ ◯ ◯ ◯ 10 0.015 98 — 22 0.8 0.20 0.19 1.05 X Δ ◯ ⊚ ◯ 110.15 100 — 23 0.7 0.26 0.24 1.08 X Δ ◯ ⊚ ◯ 12 0.1 100 — 25 0.9 0.35 0.211.67 Δ Δ ⊚ ⊚ ◯ 13 0.05 100 — 23 1.1 0.31 0.19 1.63 Δ Δ ⊚ ⊚ ◯ 14 0.015 96— 22 1.6 0.24 0.14 1.71 X Δ ◯ ⊚ ◯ 15 0.15 100 — 92 1.1 0.21 0.12 1.75 XX ◯ X ◯ 16 0.05 100 — 45 1.4 0.34 0.21 1.62 Δ X ⊚ X ◯

(Evaluation Results)

The bonding wires according to Working Examples 1 through 59 eachinclude a Cu alloy core material and a Pd coating layer formed on asurface of the Cu alloy core material, and a thickness of the Pd coatinglayer is in the preferable range of 0.015 to 0.150 μm. All of themexhibit favorable FAB shape. Further, these bonding wires contain atleast one element selected from Ni, Zn, Rh, In, Ir and Pt and aconcentration of the elements in total is 0.011 to 2% by mass relativeto the entire wire, and with this configuration, they achieve favorablehigh-temperature reliability of the ball bonded part in the HTSevaluation.

In the working examples, the area reduction rate at the time of wiredrawing was 10% or more, and the heat treatment temperature after wiredrawing was a low temperature of 500° C. or less, whereby, the crystalorientation <100> angled at 15 degrees or less to the wire longitudinaldirection among the crystal orientations in the wire longitudinaldirection could be 30% or more when measuring crystal orientations onthe cross-section of the core material in the direction perpendicular tothe wire axis of the bonding wire, and the average crystal grain size inthe cross-section of the core material in the direction perpendicular tothe wire axis of the bonding wire could be 0.9 to 1.5 μm. Consequently,the strength ratio (=ultimate strength/0.2% offset yield strength) inall cases was in the range of 1.1 to 1.6 even though the wire containedNi, Zn, Rh, In, Ir and Pt. Consequently, the wedge bondability wasfavorable in all cases.

In contrast, in Comparative Examples 4 through 7 and 12 through 14, theheat treatment temperature was a high temperature of 600° C. or more,whereby the <100> orientation proportion in the wire longitudinaldirection was less than 30%. In Comparative Examples 2, 6, 8, 9 and 14,the heat treatment temperature was a high temperature of 620° C. ormore, whereby the <100> orientation proportion in the wire longitudinaldirection was less than 30%, and the average crystal grain size in thecross-section of the core material was more than 1.5 μm. Consequently,in all Comparative Examples 2, 4 through 9 and 12 through 14, thestrength ratio was more than 1.6, and the wedge bondability was faultyor problematic.

In Comparative Examples 1 and 3, the average crystal grain size in thecross-section of the core material was less than 0.9 μm, the strengthratio was less than 1.1, and the wedge bondability was faulty in bothcases because the die area reduction rate was less than 10%. InComparative Examples 10 and 11, the <100> orientation proportion in thewire longitudinal direction was less than 30%, and the average crystalgrain size in the cross-section of the core material was less than 0.9μm, and the wedge bondability was faulty in both cases. In ComparativeExample 15, the average crystal grain size was 0.9 to 1.5 μm and the<100> orientation proportion in the wire longitudinal direction was 30%or more, but all of HTS, HAST and wedge bondability were faulty becausethe element that provides bonding reliability in a high-temperatureenvironment was not contained therein. In Comparative Example 16, HTSand HAST were faulty because the element that provides bondingreliability in a high-temperature environment was not contained therein.

Working Examples 2-1 to 2-44

(Sample)

First, the following describes a method for manufacturing a sample. ForCu as a raw material of the core material, Cu with a purity of 99.99% bymass or more and containing inevitable impurities as the remainder wasused. For Ga, Ge, Ni, Ir, Pt, Pd, B, P and Mg, the ones with purity of99% by mass or more and containing inevitable impurities as theremainder were used. Ga, Ge, Ni, Ir, Pt, Pd, B, P and Mg as additiveelements to the core material are mixed so that the wire or the corematerial will have a desired composition. Regarding the addition of Ga,Ge, Ni, Ir, Pt, Pd, B, P and Mg, they can be mixed singly.Alternatively, they may be mixed so as to be a desired amount using a Cumaster alloy containing the additive elements manufactured in advance ifthe element has a high melting point as a single body or if the elementis added in an infinitesimal amount.

The Cu alloy as the core material was manufactured by charging rawmaterials into a carbon crucible worked into a cylindrical shape with adiameter of 3 to 6 mm, heating and melting the raw materials at 1,090 to1,300° C. in vacuum or in an inert atmosphere such as an N₂ or Ar gasusing a high-frequency furnace, and performing furnace cooling. Theobtained alloy with a diameter of 3 to 6 mm was drawn to be worked intoa diameter of 0.9 to 1.2 mm, and a wire with a diameter of 300 to 600 μmwas manufactured by successively performing wire drawing using dies. Acommercially available lubricant was used for the wire drawing, and awire drawing speed was 20 to 150 m/min. In order to remove an oxide filmon a surface of wire, pickling treatment with sulfuric acid wasperformed, and a Pd coating layer was formed by 1 to 15 μm so as tocover the entire surface of the Cu alloy as the core material.Furthermore, for some wires, an alloy skin layer containing Au and Pdwas formed by 0.05 to 1.5 μm on the Pd coating layer. For the formationof the Pd coating layer and the alloy skin layer containing Au and Pd,electroplating was used. A commercially available semiconductor platingsolution was used for a plating solution. Heat treatment at 200 to 500°C. and wire drawing were then repeatedly performed to be worked into adiameter of 20 μm. After working, heat treatment was performed whileflowing an N₂ or Ar gas so that breaking elongation will finally beabout 5 to 15%. A method of heat treatment was performed whilesuccessively sweeping the wire and was performed while flowing an N₂ orAr gas. A wire feeding speed was 20 to 200 m/min, a heat treatmenttemperature was 200 to 600° C., and a heat treatment time was 0.2 to 1.0second.

For the concentration analysis of the Pd coating layer and the alloyskin layer containing Au and Pd, the analysis was performed using anAuger electron spectroscopic apparatus while sputtering the bonding wirefrom its surface in the depth direction with Ar ions. The thicknesses ofthe coating layer and the skin alloy layer were determined from anobtained concentration profile (the unit of the depth was in terms ofSiO₂) in the depth direction. A region in which a concentration of Pdwas 50 at % or more and a concentration of Au was less than 10 at % wasdetermined to be the Pd coating layer, and a region in which aconcentration of Au was in a range of 10 at % or more on a surface ofthe Pd coating layer was determined to be the alloy skin layer. Thethicknesses of the coating layer and the alloy skin layer and a maximumconcentration of Pd are listed in Tables 5 and 6. The concentration ofPd in the Cu alloy core material was measured by a method that exposes across-section of wire and performs line analysis, point analysis, or thelike on the exposed cross-section of wire by an electron probe microanalyzer installed in a scanning electron microscope. For the method forexposing the cross-section of wire, mechanical polishing, ion etching,or the like was used. For the concentrations of Ga, Ge, Ni, Ir, Pt, B, Pand Mg in the bonding wire, a solution obtained by dissolving thebonding wire with a strong acid was analyzed using an ICP emissionspectrometer or an ICP mass spectrometer, and they were detected as theconcentrations of the elements contained in the entire bonding wire.

The configurations of the respective samples manufactured according tothe above procedure are listed in the following Tables 5 and 6.

TABLE 5 Coating layer Additive element Pd M_(B) M_(B) M_(A) Other Thick-maximum Ga Ge in Ni Pd Pt Ir B P Mg ness concentration No. (% by mass)total (% by mass) (ppm by mass) (μm) (at %) Working 2-1 0.020 0.020 0.15100 Example 2-2 0.025 0.025 0.015 98 2-3 0.500 0.500 0.1 100 2-4 1.5001.500 0.05 100 2-5 0.011 0.011 0.1 100 2-6 0.025 0.025 0.05 100 2-70.300 0.300 0.05 100 2-8 1.500 1.500 0.1 100 2-9 0.015 0.011 0.026 0.05100 2-10 0.050 0.600 0.650 0.05 100 2-11 0.600 0.850 1.450 0.05 100 2-120.002 0.800 0.802 0.05 100 2-13 0.030 0.030 0.50 0.15 100 2-14 0.0300.030 1.20 0.15 100 2-15 0.030 0.030 0.50 0.05 100 2-16 0.030 0.030 1.200.1 100 2-17 0.030 0.030 0.50 0.05 100 2-18 0.030 0.030 1.20 0.1 1002-19 0.030 0.030 0.50 0.015 96 2-20 0.030 0.030 1.20 0.1 100 2-21 0.0300.80 0.15 100 2-22 0.030 1.20 0.05 100 Thick- Mechanical characteristicsness Crystal structure 0.2% of <100> Average Ulti- Offset alloyProportion crystal mate yield Strength skin of wire C grain strengthstrength ratio Wire quality layer section size {circle around (1)}{circle around (2)} {circle around (1)}/{circle around (2)} Wedge FABCrushed No. (μm) (%) (μm) (mN/μm²) — bondability HTS shape HAST shapeLeaning Working 2-1 — 91 1.1 0.20 0.19 1.05 ⊚ Δ ◯ Δ ◯ ⊚ Example 2-20.0005 71 1.2 0.23 0.17 1.35 ⊚ Δ ◯ ◯ ◯ ⊚ 2-3 0.0005 70 0.9 0.25 0.181.39 ⊚ Δ ⊚ ⊚ ◯ ⊚ 2-4 0.001 71 1.0 0.30 0.23 1.30 ⊚ Δ ⊚ ⊚ ◯ ⊚ 2-5 0.00174 1.1 0.31 0.23 1.35 ⊚ Δ ⊚ Δ ◯ ⊚ 2-6 0.08 62 1.1 0.32 0.25 1.28 ⊚ Δ Δ ◯◯ ⊚ 2-7 0.01 74 1.3 0.34 0.26 1.31 ⊚ Δ ⊚ ⊚ ◯ ⊚ 2-8 0.01 64 1.0 0.35 0.301.17 ⊚ Δ ⊚ ⊚ ◯ ⊚ 2-9 0.001 50 1.2 0.34 0.22 1.55 ⊚ Δ ⊚ Δ ◯ ⊚ 2-10 0.0196 0.9 0.21 0.19 1.11 ⊚ Δ ⊚ ⊚ ◯ ⊚ 2-11 0.003 79 1.0 0.22 0.16 1.38 ⊚ Δ ⊚⊚ ◯ ⊚ 2-12 0.003 69 1.0 0.23 0.19 1.21 ⊚ Δ ⊚ ⊚ ◯ ⊚ 2-13 0.001 53 1.10.30 0.19 1.58 ⊚ ◯ ⊚ ◯ ◯ ⊚ 2-14 0.003 90 1.2 0.27 0.25 1.08 ⊚ ⊚ ⊚ ◯ ◯ ⊚2-15 — 70 1.2 0.28 0.21 1.33 ⊚ ◯ ⊚ ◯ ◯ ⊚ 2-16 0.01 68 1.0 0.29 0.25 1.16⊚ ⊚ ⊚ ◯ ◯ ⊚ 2-17 0.01 69 1.1 0.32 0.26 1.23 ⊚ ◯ ⊚ ◯ ◯ ⊚ 2-18 0.01 75 1.30.33 0.25 1.32 ⊚ ⊚ ⊚ ◯ ◯ ⊚ 2-19 0.0005 63 1.2 0.34 0.28 1.21 ⊚ ◯ ⊚ ◯ ◯ ⊚2-20 0.01 73 1.0 0.31 0.23 1.35 ⊚ ⊚ ⊚ ◯ ◯ ⊚ 2-21 0.01 63 1.0 0.34 0.291.17 ⊚ ◯ ⊚ ◯ ◯ ⊚ 2-22 0.003 51 1.0 0.21 0.14 1.50 ⊚ ⊚ ⊚ ◯ ◯ ⊚

TABLE 6 Coating layer Additive element Pd M_(B) M_(B) M_(A) other Thick-maximum Ga Ge in Ni Pd Pt Ir B P Mg ness concentration No. (% by mass)total (% by mass) (ppm by mass) (μm) (at %) Working 2-23 0.030 0.0300.80 0.05 100 Example 2-24 0.030 0.030 1.20 0.15 100 2-25 0.030 0.0300.80 0.15 100 2-26 0.030 0.030 1.20 0.15 100 2-27 0.030 0.030 0.80 0.01597 2-28 0.030 0.030 1.20 0.1 100 2-29 0.500 0.500 0.90 30 0.05 100 2-300.500 0.500 0.90 30 0.05 100 2-31 0.500 0.500 0.90 50 0.05 100 2-320.500 0.500 0.90 50 0.15 100 2-33 0.500 0.500 0.90 10 0.15 100 2-340.500 0.500 0.90 10 0.15 100 2-35 0.800 0.500 1.300 0.50 15 0.015 992-36 0.080 1.200 1.280 0.50 15 0.15 100 2-37 1.300 0.050 1.350 0.50 1000.15 100 2-38 0.300 0.500 0.800 0.50 100 0.015 96 2-39 0.080 0.040 0.1200.50 30 0.015 98 2-40 1.000 0.100 1.100 0.50 30 0.15 100 2-41 0.0500.015 98 2-42 0.050 0.015 96 2-43 1.000 0.1 100 2-44 1.000 0.1 100Thick- Mechanical characteristics ness Crystal structure 0.2% of <100>Average Offset alloy Proportion crystal Ultimate yield Strength skin ofwire C grain strength strength ratio Wire quality layer section size{circle around (1)} {circle around (2)} {circle around (1)}/{circlearound (2)} Wedge FAB Crushed No. (μm) (%) (μm) (mN/μm²) — bondabilityHTS shape HAST shape Leaning Working 2-23 0.01 97 1.2 0.24 0.22 1.09 ⊚ ◯◯ ◯ ◯ ⊚ Example 2-24 0.001 84 0.9 0.29 0.20 1.45 ⊚ ⊚ ⊚ ◯ ◯ ⊚ 2-25 0.0873 1.0 0.30 0.23 1.30 ⊚ ◯ Δ ◯ ◯ ⊚ 2-26 0.001 50 1.1 0.28 0.18 1.56 ⊚ ⊚ ⊚◯ ◯ ⊚ 2-27 0.003 87 1.3 0.34 0.23 1.48 ⊚ ◯ ⊚ ◯ ◯ ⊚ 2-28 0.003 76 1.10.30 0.22 1.36 ⊚ ⊚ ⊚ ◯ ◯ ⊚ 2-29 0.003 66 0.9 0.26 0.21 1.24 ⊚ ◯ ⊚ ⊚ ⊚ ⊚2-30 — 65 1.2 0.29 0.24 1.21 ⊚ ◯ ⊚ ⊚ ⊚ ⊚ 2-31 0.003 92 1.2 0.32 0.291.10 ⊚ ◯ ⊚ ⊚ ⊚ ⊚ 2-32 0.01 72 1.2 0.33 0.25 1.32 ⊚ ◯ ⊚ ⊚ ⊚ ⊚ 2-33 0.00154 1.1 0.31 0.2 1.55 ⊚ ◯ ⊚ ⊚ ⊚ ⊚ 2-34 0.01 81 1.0 0.25 0.17 1.47 ⊚ ◯ ⊚ ⊚⊚ ⊚ 2-35 0.003 73 1.2 0.33 0.25 1.32 ⊚ ◯ ◯ ⊚ ⊚ ⊚ 2-36 0.01 76 1.3 0.290.22 1.32 ⊚ ◯ ⊚ ⊚ ⊚ ⊚ 2-37 0.01 91 0.9 0.26 0.24 1.08 ⊚ ◯ ⊚ ⊚ ⊚ ⊚ 2-380.003 67 1.0 0.23 0.2 1.15 ⊚ ◯ ◯ ⊚ ⊚ ⊚ 2-39 0.001 91 1.1 0.33 0.3 1.10 ⊚◯ ◯ ⊚ ⊚ ⊚ 2-40 0.05 67 1.2 0.29 0.25 1.16 ⊚ ◯ ⊚ ⊚ ⊚ ⊚ 2-41 — 57 1.1 0.290.19 1.53 ⊚ Δ ◯ ⊚ ◯ ⊚ 2-42 — 98 1.0 0.26 0.23 1.13 ⊚ Δ ◯ ⊚ ◯ ⊚ 2-43 — 751.0 0.35 0.26 1.35 ⊚ Δ ⊚ ⊚ ◯ ⊚ 2-44 — 69 1.2 0.21 0.18 1.17 ⊚ Δ ⊚ ⊚ ◯ ⊚

(Method of Evaluation)

A crystal structure was evaluated on a surface of wire as an observationsurface. Electron backscattered diffraction (EBSD) method was used as amethod of evaluation. The EBSD method is characterized in that it canobserve crystal orientations on an observation surface and cangraphically show an angle difference of the crystal orientations betweenadjacent measurement points. Further, the EBSD method can relativelyeasily observe the crystal orientations with high accuracy even for athin wire like the bonding wire.

Care should be taken when performing EBSD with a curved surface like thewire surface as an observation subject. When a region with a largecurvature is measured, measurement with high accuracy is difficult.However, a bonding wire to be measured is fixed to a line on a plane,and a flat part near the center of the bonding wire is measured, wherebymeasurement with high accuracy can be performed. Specifically, thefollowing measurement region will work well. The size in thecircumferential direction is 50% or less of the wire diameter with thecenter in the wire longitudinal direction as an axis, whereas the sizein the wire longitudinal direction is 100 μm or less. Preferably, thesize in the circumferential direction is 40% or less of the wirediameter, whereas the size in the wire longitudinal direction is 40 μmor less, whereby measurement efficiency can be improved by reducing ameasurement time. In order to further improve accuracy, it is desirablethat three or more points be measured to obtain average information withvariations taken into account. The measurement sites may be apart fromeach other by 1 mm or more so as not to be close to each other.

As for the orientation proportion of the crystal orientation <100>angled at 15 degrees or less to the wire longitudinal direction amongthe crystal orientations in the wire longitudinal direction in thecross-section of the core material in the direction perpendicular to thewire axis of the bonding wire and the average crystal grain size (μm) inthe cross-section of the core material in the direction perpendicular tothe wire axis, they were obtained by the same method as Working Examples1 to 59. As for 0.2% offset yield strength and ultimate strength, theywere evaluated by the same method as Working Examples 1 to 59 and astrength ratio was calculated by the above-mentioned equation (1).

The bonding reliability of the ball bonded part in a high-temperatureand high humidity environment or a high-temperature environment wasdetermined by manufacturing a sample for bonding reliability evaluation,performing HAST and HTS evaluation, and evaluating the bonding longevityof the ball bonded part in each test. The sample for bonding reliabilityevaluation was manufactured by performing ball bonding onto anelectrode, which has been formed by forming an alloy of Al-1.0% Si-0.5%Cu as a film with a thickness of 0.8 μm on a Si substrate on a generalmetallic frame, using a commercially available wire bonder and sealingit with a commercially available epoxy resin. A ball was formed whileflowing an N₂+5% H₂ gas at a flow rate of 0.4 to 0.6 L/min, and its sizewas within the range of a diameter of 33 to 34 μm.

For the HAST evaluation, the manufactured sample for bonding reliabilityevaluation was exposed to a high-temperature and high-humidityenvironment with a temperature of 130° C. and a relative humidity of 85%using an unsaturated type pressure cooker tester and was biased with 7V. A shear test on the ball bonded part was performed every 48 hours,and a time until a value of shear strength became half of the initialshear strength was determined to be the bonding longevity of the ballbonded part. The shear test after the high-temperature and high-humiditytest was performed after removing the resin by acid treatment andexposing the ball bonded part.

A tester manufactured by DAGE was used for a shear tester for the HASTevaluation. An average value of measurement values of 10 ball bondedparts randomly selected was used for the value of the shear strength. Inthe above evaluation, the bonding longevity being less than 96 hours wasdetermined to be practically problematic to be marked with a symbol of“cross,” being 96 hours or more and less than 144 hours was determinedto be practicable but somewhat problematic to be marked with a symbol of“triangle,” being 144 hours or more and less than 288 hours wasdetermined to be practically no problem to be marked with a symbol of“circle,” and being 288 hours or more was determined to be excellent tobe marked with a symbol of “double circle” in the column “HAST” inTables 5 and 6.

For the HTS evaluation, the manufactured sample for bonding reliabilityevaluation was exposed to a high-temperature environment with atemperature of 200° C. using a high-temperature thermostatic device. Ashear test on the ball bonded part was performed every 500 hours, and atime until a value of shear strength became half of the initial shearstrength was determined to be the bonding longevity of the ball bondedpart. The shear test after the high-temperature and high-humidity testwas performed after removing the resin by acid treatment and exposingthe ball bonded part.

A tester manufactured by DAGE was used for a shear tester for the HTSevaluation. An average value of measurement values of 10 ball bondedparts randomly selected was used for the value of the shear strength. Inthe above evaluation, the bonding longevity being 500 hours or more andless than 1,000 hours was determined to be practicable but be desired tobe improved to be marked with a symbol of “triangle,” being 1,000 hoursor more and less than 3,000 hours was determined to be practically noproblem to be marked with a symbol of “circle,” and being 3,000 hours ormore was determined to be especially excellent to be marked with asymbol of “double circle.”

For the evaluation of ball formability (FAB shape), a ball beforeperforming bonding was collected and observed, and the presence orabsence of voids on the ball surface and the presence or absence ofdeformation of the ball, which is primarily a perfect sphere, weredetermined. The occurrence of any of the above was determined to befaulty. The formation of the ball was performed while blowing an N₂ gasat a flow rate of 0.5 L/min in order to reduce oxidation in a meltingprocess. The size of the ball was 34 μm. For one condition, 50 ballswere observed. A SEM was used for the observation. In the evaluation ofthe ball formability, a case in which five or more failures occurred wasdetermined to be problematic to be marked with a symbol of “cross,” acase of three or four failures was determined to be practicable butsomewhat problematic to be marked with a symbol of “triangle,” a case ofone or two failures was determined to be no problem to be marked with asymbol of “circle,” and a case in which no failure occurred wasdetermined to be excellent to be marked with Aa symbol of “doublecircle” in the column “FAB shape” in Tables 5 and 6.

The evaluation of wedge bondability on the wire bonded part wasdetermined by performing 1,000 pieces of bonding on leads of a leadframe and by the occurrence frequency of peeling of the bonded part. AnFe-42 at % Ni alloy lead frame plated with 1 to 3 μm Ag was used for thelead frame. In this evaluation, assuming bonding conditions morerigorous than normal, a stage temperature was set to 150° C., which waslower than a general set temperature range. In the evaluation, a case inwhich 11 or more failures occurred was determined to be problematic tobe marked with a symbol of “cross,” a case of 6 to 10 failures wasdetermined to be practicable but somewhat problematic to be marked witha symbol of “triangle,” a case of 1 to 5 failures was determined to beno problem to be marked with a symbol of “circle,” and a case in whichno failure occurred was determined to be excellent to be marked with asymbol of “double circle” in the column “wedge bondability” in Tables 5and 6.

The evaluation of a crushed shape of the ball bonded part was determinedby observing the ball bonded part from immediately above after bondingand evaluating by its circularity. For a bonding counterpart, anelectrode in which an Al-0.5% Cu alloy was formed as a film with athickness of 1.0 μm on a Si substrate was used. The observation wasperformed using an optical microscope, and 200 sites were observed forone condition. Being elliptic with large deviation from a perfect circleand being anisotropic in deformation were determined to be faulty in thecrushed shape of the ball bonded part. In the above evaluation, a casein which six or more failures occurred was determined to be problematicto be marked with a symbol of “cross,” a case of four or five failureswas determined to be practicable but somewhat problematic to be markedwith a symbol of “triangle,” being one to three was determined to be noproblem to be marked with a symbol of “circle,” and a case in which afavorable perfect circle was obtained for all was determined to beespecially excellent to be marked with a symbol of “double circle” inthe column “crushed shape” in Tables 5 and 6.

[Leaning]

To a lead frame for evaluation, 100 pieces of bonding were performedwith a loop length of 5 mm and a loop height of 0.5 mm. As a method ofevaluation, a wire upright part was observed from a chip horizontaldirection, and evaluation was performed based on spacing when spacingbetween a perpendicular line passing through the center of the ballbonded part and the wire upright part was maximized (leaning spacing).If the leaning spacing was smaller than the wire diameter, leaning wasdetermined to be favorable, whereas if the leaning spacing was larger,the upright part leaned, and the leaning was determined to be faulty.One hundred bonded wires were observed with an optical microscope, andthe number of leaning failures was counted. A case in which seven ormore failures occurred was determined to be problematic to be markedwith a symbol of “cross,” a case of four to six failures was determinedto be practicable but somewhat problematic to be marked with a symbol of“triangle,” a case of one to three failures was determined to be noproblem to be marked with a symbol of “circle,” and a case in which nofailure occurred was determined to be excellent to be marked with asymbol of “double circle” in the column “leaning” in Tables 5 and 6.

(Evaluation Results)

As shown in Tables 5 and 6, the bonding wires of Working Examples 2-1through 2-44 each include the Cu alloy core material and the Pd coatinglayer formed on the surface of the Cu alloy core material, and thebonding wire contains one or more elements selected from Ga and Ge and aconcentration of the elements in total is 0.011 to 1.5% by mass relativeto the entire wire. It has been revealed that with this configurationthe bonding wires of Working Examples 2-1 through 2-44 can obtain thereliability of the ball bonded part in the HAST test in thehigh-temperature and high-humidity environment with a temperature of130° C. and a relative humidity of 85%.

In the working examples of the present invention further including thealloy skin layer containing Au and Pd on the Pd coating layer, it hasbeen revealed that excellent wedge bondability can be obtained when thelayer thickness of the alloy skin layer containing Au and Pd is 0.0005to 0.050 μm.

In the working examples in which the bonding wires further contain atleast one element selected from Ni, Ir, Pt and Pd, it has been revealedthat the high-temperature reliability of the ball bonded part in the HTSevaluation is further favorable.

In the working examples in which the bonding wires further contain atleast one element selected from B, P and Mg, the crushed shape of theball bonded part was favorable when a concentration of each of theelements was 1 to 200 ppm by mass relative to the entire wire.

Working Examples 3-1 to 3-50

(Sample)

First, there will be described a method for manufacturing a sample. ForCu as a raw material of a core material, Cu with a purity of 99.99% bymass or more and containing inevitable impurities as the remainder wasused. For As, Te, Sn, Sb, Bi, Se, Ni, Zn, Rh, In, Ir, Pt, Ga, Ge, Pd, B,P, Mg, Ca and La, the ones with a purity of 99% by mass or more andcontaining inevitable impurities as the remainder were used. As, Te, Sn,Sb, Bi, Se, Ni, Zn, Rh, In, Ir, Pt, Ga, Ge, Pd, B, P, Mg, Ca and La asadditive elements to the core material are mixed so that the wire or thecore material will have a desired composition. Regarding the addition ofAs, Te, Sn, Sb, Bi, Se, Ni, Zn, Rh, In, Ir, Pt, Ga, Ge, Pd, B, P, Mg, Caand La, they can be mixed singly. Alternatively, they may be mixed so asto be a desired amount using a Cu master alloy containing the additiveelements manufactured in advance if the element has a high melting pointas a single body or if the element is added in an infinitesimal amount.

The Cu alloy for the core material was manufactured by charging the rawmaterials into a carbon crucible worked into a cylindrical shape with adiameter of 3 to 6 mm, heating and melting the raw materials at 1,090 to1,300° C. in vacuum or in an inert atmosphere such as an N₂ or Ar gasusing a high-frequency furnace, and performing furnace cooling. Theobtained alloy with a diameter of 3 to 6 mm was drawn to manufacture awire with a diameter of 0.9 to 1.2 mm. Thereafter, a wire with adiameter of 300 to 600 μm was manufactured by successively performingwire drawing and the like using a die. A commercially availablelubricant was used for the wire drawing, and a wire drawing speed was 20to 150 m/min. In order to remove an oxide film on a surface of wire, apickling treatment with hydrochloric acid was performed, and a Pdcoating layer was formed by 1 to 15 μm so as to cover the entire surfaceof the Cu alloy as the core material. Furthermore, for some wires, analloy skin layer containing Au and Pd was formed by 0.05 to 1.5 μm onthe Pd coating layer. For the formation of the Pd coating layer and thealloy skin layer containing Au and Pd, electroplating was used. Acommercially available semiconductor plating solution was used for aplating solution. Heat treatment at 200 to 500° C. and wire drawing werethen repeatedly carried out to perform working to a diameter of 20 μm.After working, heat treatment was performed while flowing an N₂ or Argas so that breaking elongation will finally be about 5 to 15%. A methodof heat treatment was performed while successively sweeping the wire andwas carried out while flowing an N₂ or Ar gas. A wire feeding speed was20 to 200 m/min, a heat treatment temperature was 200 to 600° C., and aheat treatment time was 0.2 to 1.0 second.

For a concentration analysis of the Pd coating layer and the alloy skinlayer containing Au and Pd, an Auger electron spectrometry was performedwhile trimming the bonding wire from its surface in the depth directionby sputtering or the like. From an obtained concentration profile in thedepth direction, there were determined a thickness of the Pd coatinglayer, a thickness of the alloy skin layer containing Au and Pd and amaximum concentration of Pd.

Concerning Working Examples 3-1 to 3-50, an element selected from As,Te, Sn, Sb, Bi and Se is contained in the core material.

Concerning Working Examples 3-34 through 3-44, Cu is caused to bepresent at an outermost surface of the bonding wire. In this regard, acolumn of “Cu concentration at wire surface” is provided in Table 7, andresults obtained by measuring a surface of the bonding wire by an Augerelectron spectroscopic apparatus were entered therein. By selecting atemperature and time for heat treatment of the bonding wire, Cu wascaused to be present at an outermost surface at a certain concentration.Concerning Working Examples 3-1 through 3-33 and 3-45 through 3-50, heattreatment conditions that caused Cu not to be present at an outermostsurface were applied, and therefore Cu was not detected by the Augerelectron spectroscopic apparatus.

The configurations of the samples manufactured according to the aboveprocedure are listed in Tables 7 and 8.

TABLE 7 Additive element M_(A) M_(B) M_(C) M_(C) Ni Pd Pt Zn Rh In Ir GnGe As Te Sn Sb Bi Se in (% by mass) No. (ppm by mass) total (Amount incore material for Pd (% by mass)) Working 3-1 0.4 0.4 Example 3-2 1.21.2 3-3 12 12 3-4 75 75 3-5 0.1 0.1 3-6 1.2 1.2 3-8 15 15 3-8 98 98 3-90.2 0.2 3-10 1.3 1.3 3-11 10 10 3-12 0.1 0.1 3-13 1.2 1.2 3-14 9.8 9.83-15 0.3 0.3 3-16 1 1 3-17 0.1 0.1 3-18 1.2 1.2 3-19 4.9 4.9 3-20 99 993-21 0.1 0.1 0.05 3-22 4.1 4.1 1.2 3-23 8.1 8.1 0.7 3-24 12 12 0.7 3-2518 18 0.7 Crystal structure Thick <100> Mechanical characteristics ness-Proportion 0.2% Coating layer of of Average Offset Additive element Pdalloy wire crystal Ultimate yield Strength Other Thick- maximum skin Cgrain strength strength ratio Wire quality B P Mg Ca La nessconcentration layer section size {circle around (1)} {circle around (2)}{circle around (1)}/{circle around (2)} Wedge FAB Crushed No. (ppm bymass) (μm) (at %) (μm) (%) (μm) (mN/μm²) — bondability HTS shape HASTshape Leaning Working 3-1 0.1 100 0.01 94 0.9 0.33 0.22 1.50 ⊚ Δ ⊚ ◯ ◯ ⊚Example 3-2 0.15 100 0.05 74 1.0 0.29 0.22 1.32 ⊚ Δ ◯ ⊚ ◯ ◯ 3-3 0.01 100— 73 1.1 0.25 0.19 1.32 ⊚ Δ Δ ⊚ ◯ ⊚ 3-4 0.05 100 0.001 75 1.2 0.22 0.171.29 ⊚ Δ ⊚ ⊚ ◯ ⊚ 3-5 0.015 98 0.0005 77 1.3 0.32 0.24 1.33 ⊚ Δ ◯ ◯ ◯ ⊚3-6 0.1 100 0.001 65 1.0 0.28 0.23 1.22 ⊚ Δ ⊚ ⊚ ◯ ◯ 3-8 0.15 100 0.00377 0.9 0.33 0.25 1.32 ⊚ Δ ◯ ⊚ ◯ ⊚ 3-8 0.01 100 0.01 84 1.2 0.31 0.211.48 ⊚ Δ Δ ⊚ ◯ ⊚ 3-9 0.015 97 0.05 98 1.2 0.32 0.21 1.52 ⊚ Δ ◯ ◯ ◯ ◯3-10 0.05 100 — 54 1.1 0.29 0.26 1.12 ⊚ Δ ⊚ ⊚ ◯ ⊚ 3-11 0.1 100 0.005 501.2 0.23 0.21 1.10 ⊚ Δ ⊚ ⊚ ◯ ⊚ 3-12 0.15 100 0.001 66 1.0 0.19 0.16 1.19⊚ Δ ◯ ◯ ◯ ◯ 3-13 0.015 95 0.003 87 1.1 0.30 0.21 1.43 ⊚ Δ ◯ ⊚ ◯ ⊚ 3-140.05 100 0.01 93 0.9 0.35 0.22 1.59 ⊚ Δ ⊚ ⊚ ◯ ⊚ 3-15 0.1 100 0.05 54 1.10.20 0.18 1.11 ⊚ Δ ⊚ ◯ ◯ ◯ 3-16 0.15 100 0.001 78 1.2 0.30 0.23 1.30 ⊚ Δ◯ ⊚ ◯ ⊚ 3-17 0.015 99 0.003 65 1.2 0.25 0.20 1.25 ⊚ Δ ◯ ◯ ◯ ⊚ 3-18 0.05100 0.01 52 1.3 0.21 0.19 1.11 ⊚ Δ ⊚ ⊚ ◯ ◯ 3-19 0.1 100 0.05 60 1.1 0.260.22 1.18 ⊚ Δ ⊚ ⊚ ◯ ⊚ 3-20 0.15 100 — 90 1.2 0.30 0.19 1.58 ⊚ Δ ◯ ⊚ ◯ ⊚3-21 0.015 97 — 55 1.3 0.19 0.17 1.12 ⊚ ◯ ◯ ⊚ ◯ ⊚ 3-22 100 0.1 100 0.00190 0.9 0.32 0.21 1.52 ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ 3-23 100 0.1 100 0.003 68 0.9 0.250.20 1.25 ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ 3-24 50 0.05 100 0.05 60 1.0 0.24 0.20 1.20 ⊚ ⊚ ⊚⊚ ⊚ ⊚ 3-25 50 0.15 100 0.003 85 1.0 0.30 0.21 1.43 ⊚ ⊚ ◯ ⊚ ⊚ ⊚

TABLE 8 Additive element M_(A) M_(B) M_(C) M_(C) Ni Pd Pt Zn Rh In Ir GaGe Other As Te Sn Sb Bi Se in (% by mass) B P No. (ppm by mass) total(Amount in core material for Pd (% by mass)) (ppm by mass) Working 3-2652 52 0.05 Example 3-27 99 99 0.1 3-28 0.2 0.2 0.1 0.05 3-29 2.5 2.5 1.10.05 100 3-30 5.2 5.2 1.1 0.1 100 3-31 21 21 0.7 0.1 50 3-32 41 41 1.10.05 3-33 98 98 0.1 0.1 3-34 22 22 3-35 16 16 1.1 0.1 3-36 4.1 4.1 3-375.8 5.8 0.7 0.7 3-38 0.7 0.7 3-39 4.8 4.8 1.1 1.1 3-40 2.5 2.5 0.7 0.13-41 1.8 1.8 0.1 0.05 3-42 0.5 0.5 1.1 0.05 3-43 0.2 0.2 0.05 0.1 3-4420 20 0.7 0.02 3-45 1.0 1 3-46 1.5 1.5 3-47 1.2 1.2 3-48 1.0 1 3-49 0.90.9 3-50 1.2 1.2 Crystal structure Thick <100> Mechanicalcharacteristics ness- Proportion 0.2% Coating layer of of Average OffsetCu Additive element Pd alloy wire crystal Ultimate yield Strengthconcentration Other Thick- maximum skin C grain strength strength ratioWire quality at wire Mg Ca La ness concentration layer section size{circle around (1)} {circle around (2)} {circle around (1)}/{circlearound (2)} Wedge FAB Crushed surface No. (ppm by mass) (μm) (at %) (μm)(%) (μm) (mN/μm²) — bondability HTS shape HAST shape Leaning (at %)Working 3-26 50 0.1 100 0.0005 72 1.2 0.27 0.21 1.29 ⊚ ◯ ⊚ ⊚ ⊚ ⊚ Example3-27 0.01 100 0.01 92 1.1 0.34 0.22 1.55 ⊚ ◯ Δ ⊚ ◯ ⊚ 3-28 0.05 100 0.00598 1.3 0.25 0.16 1.56 ⊚ ◯ ⊚ ⊚ ◯ ⊚ 3-29 0.1 100 0.003 65 1.1 0.24 0.201.20 ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ 3-30 0.1 100 0.001 74 1.1 0.30 0.22 1.36 ⊚ ⊚ ⊚ ⊚ ⊚ ⊚3-31 0.15 100 0.003 52 1.2 0.23 0.21 1.10 ⊚ ⊚ ◯ ⊚ ⊚ ⊚ 3-32 1 0.05 1000.05 88 1.0 0.32 0.22 1.45 ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ 3-33 0.01 100 0.01 60 1.0 0.210.18 1.17 ⊚ ◯ Δ ⊚ ◯ ⊚ 3-34 0.1 100 0.001 87 1.1 0.30 0.21 1.43 ⊚⊚ Δ ⊚ ◯◯ ◯ 5.4 3-35 0.15 100 0.003 65 1.3 0.28 0.24 1.17 ⊚⊚ ⊚ ◯ ◯ ◯ ⊚ 5.2 3-360.01 100 0.01 54 0.9 0.23 0.21 1.10 ⊚⊚ Δ Δ ◯ ◯ ⊚ 10 3-37 0.05 100 0.0574 1.2 0.29 0.22 1.32 ⊚⊚ ⊚ ⊚ ◯ ◯ ⊚ 11 3-38 0.1 100 — 96 1.1 0.29 0.191.53 ⊚ Δ ⊚ Δ ◯ ◯ 26 3-39 0.15 100 0.0005 66 1.0 0.21 0.17 1.24 ⊚⊚ ⊚ ◯ Δ◯ ⊚ 28 3-40 0.01 100 — 88 1.0 0.33 0.23 1.43 ⊚⊚ ⊚ Δ Δ ◯ ⊚ 1.1 3-41 0.05100 0.0005 96 1.1 0.31 0.20 1.55 ⊚⊚ ⊚ ⊚ Δ ◯ ⊚ 1.4 3-42 0.1 100 0.01 540.9 0.26 0.23 1.13 ⊚ ⊚ ⊚ ◯ ◯ ⊚ 5.2 3-43 0.15 100 0.03 84 1.2 0.32 0.221.45 ⊚ ⊚ ◯ ◯ ◯ ⊚ 5.5 3-44 0.01 100 0.01 85 1.2 0.29 0.20 1.45 ⊚⊚ ⊚ Δ ◯ ◯⊚ 12 3-45 0.1 100 — 96 1.1 0.29 0.19 1.53 ⊚ Δ ⊚ ⊚ ◯ ⊚ 3-46 0.1 100 — 571.0 0.20 0.18 1.11 ⊚ Δ ⊚ ⊚ ◯ ⊚ 3-47 0.1 100 — 77 1.3 0.30 0.23 1.30 ⊚ Δ⊚ ⊚ ◯ ⊚ 3-48 0.1 100 — 72 0.9 0.28 0.21 1.33 ⊚ Δ ⊚ ⊚ ◯ ⊚ 3-49 0.1 100 —56 1.2 0.21 0.18 1.17 ⊚ Δ ⊚ ⊚ ◯ ⊚ 3-50 0.1 100 — 61 1.0 0.22 0.18 1.22 ⊚Δ ⊚ ⊚ ◯ ⊚

(Method of Evaluation)

A crystal structure was evaluated with a surface of wire as anobservation surface. An electron backscattered diffraction method (EBSD)was used as a method of evaluation. The EBSD method is characterized inthat it can observe crystal orientations on an observation surface andgraphically shows an angle difference of the crystal orientationsbetween adjacent measurement points. The EBSD method can relativelyeasily observe the crystal orientations with high accuracy, even for athin wire like the bonding wire.

Care should be taken when performing EBSD method with a curved surfacelike the wire surface as a subject. When a region with a large curvatureis measured, measurement with high accuracy is difficult. However, abonding wire to be measured is fixed to a line on a plane, and a flatpart near the center of the bonding wire is measured, wherebymeasurement with high accuracy can be performed. Specifically, thefollowing measurement region will work well. The size in thecircumferential direction is 50% or less of the wire diameter with acenter in the wire longitudinal direction as an axis, and the size inthe wire longitudinal direction is 100 μm or less. Preferably, the sizein the circumferential direction is 40% or less of the wire diameter,and the size in the wire longitudinal direction is 40 μm or less,whereby measurement efficiency can be improved by reducing a measurementtime. In order to further improve accuracy, it is desirable that threeor more points are measured to obtain average information withvariations taken into account. The measurement sites may be apart fromeach other by 1 mm or more so as not to be close to each other.

As for the orientation proportion of the crystal orientation <100>angled at 15 degrees or less to the wire longitudinal direction amongthe crystal orientations in the wire longitudinal direction in thecross-section of the core material in the direction perpendicular to thewire axis of the bonding wire and the average crystal grain size (μm) inthe cross-section of the core material in the direction perpendicular tothe wire axis, they were obtained by the same method as Working Examples1 to 59. As for 0.2% offset yield strength and ultimate strength, theywere evaluated by the same method as Working Examples 1 to 59 and astrength ratio was calculated by the above-mentioned equation (1).

The bonding reliability of the ball bonded part in a high-temperatureand high humidity environment or a high-temperature environment wasdetermined by manufacturing a sample for bonding reliability evaluation,performing HAST and HTS evaluation, and by evaluating the bondinglongevity of the ball bonded part in each test. The sample for bondingreliability evaluation was manufactured by performing ball bonding ontoan electrode, which has been formed by forming an alloy of Al-1.0%Si-0.5% Cu as a film with a thickness of 0.8 μm on a Si substrate on ageneral metallic frame, using a commercially available wire bonder andsealing it with a commercially available epoxy resin. A ball was formedwhile flowing an N₂+5% H₂ gas at a flow rate of 0.4 to 0.6 L/min, andits size was a diameter of a range from 33 to 34 μm.

For the HAST evaluation, the manufactured sample for bonding reliabilityevaluation was exposed to a high-temperature and high-humidityenvironment of a temperature of 130° C. and a relative humidity of 85%using an unsaturated type pressure cooker tester and was biased with 5V. A shear test on the ball bonded part was performed every 48 hours,and a time until a value of shear strength became half of the initialshear strength was determined to be the bonding longevity of the ballbonded part. The shear test after the high-temperature and high-humiditytest was carried out after removing a resin by acid treatment andexposing the ball bonded part.

A tester manufactured by DAGE was used for a shear tester for the HASTevaluation. An average value of measurement values on 10 ball bondedparts randomly selected was used for the value of the shear strength. Inthe above evaluation, the bonding longevity being less than 96 hours wasdetermined to be practically problematic to be marked with a symbol of“cross,” being 96 hours or more and less than 144 hours was determinedto be practicable but somewhat problematic to be marked with a symbol of“triangle,” being 144 hours or more and less than 288 hours wasdetermined to be practically no problem to be marked with a symbol of“circle,” being 288 hours or more and less than 384 hours was determinedto be excellent to be marked with a symbol of “double circle,” and being384 hours or more was determined to be especially excellent to be markedto with a symbol of “a pair of double circle” in the column “HAST” inTables 7 and 8.

For the HTS evaluation, the manufactured sample for bonding reliabilityevaluation was exposed to a high-temperature environment of atemperature of 200° C. using a high-temperature thermostatic device. Ashear test on the ball bonded part was performed every 500 hours, and atime until a value of shear strength became half of the initial shearstrength was determined to be the bonding longevity of the ball bondedpart. The shear test after the high-temperature and high-humidity testwas performed after removing a resin by acid treatment and exposing theball bonded part.

A tester manufactured by DAGE was used for a shear tester for the HTSevaluation. An average value of measurement values on 10 ball bondedparts randomly selected was used for the value of the shear strength. Inthe above evaluation, the bonding longevity being 500 or more to lessthan 1,000 hours was determined to be practicable but desirably to beimproved to be marked with a symbol of “triangle,” being 1,000 or moreto less than 3,000 hours was determined to be practically no problem tobe marked with a symbol of “circle,” and being 3,000 hours or more wasdetermined to be especially excellent to be marked with a symbol of“double circle” in the column “HTS” in Tables 7 and 8.

For the evaluation of ball formability (FAB shape), a ball beforeperforming bonding was collected and observed, and the presence orabsence of voids on a surface of the ball and the presence or absence ofdeformation of the ball, which is primarily a perfect sphere, weredetermined. The occurrence of any of the above was determined to befaulty. The formation of the ball was performed while an N₂ gas wasblown at a flow rate of 0.5 L/min in order to reduce oxidation in amelting process. The size of the ball was 34 μm. For one condition, 50balls were observed. A SEM was used for the observation. In theevaluation of the ball formability, a case where five or more failuresoccurred was determined to be problematic to be marked with a symbol of“cross,” a case of three or four failures was determined to bepracticable but somewhat problematic to be marked with a symbol of“triangle,” a case of one or two failures was determined to be noproblem to be marked with a symbol of “circle,” and a case where nofailure occurred was determined to be excellent to be marked with asymbol of “double circle” in the column “FAB shape” in Tables 7 and 8.

The evaluation of wedge bondability on the wire bonded part wasdetermined by performing 1,000 pieces of bonding on leads of a leadframe and evaluating by the occurrence frequency of peeling of thebonded part. An Fe-42 at % Ni alloy lead frame plated with 1 to 3 μm Agwas used for the lead frame. In this evaluation, assuming more rigorousbonding conditions than normal, a stage temperature was set to be 150°C., which was lower than a generally set temperature range. In the aboveevaluation, a case where 11 or more failures occurred was determined tobe problematic to be marked with a symbol of “cross,” a case of 6 to 10failures was determined to be practicable but somewhat problematic to bemarked with a symbol of “triangle,” a case of 1 to 5 failures wasdetermined to be no problem to be marked with a symbol of “circle,” anda case where no failure occurred was determined to be excellent to bemarked with a symbol of “double circle” in the column “wedgebondability” in Tables 7 and 8.

The evaluation of a crushed shape of the ball bonded part was determinedby observing the ball bonded part from immediately above after bondingand evaluating by its circularity. For an object to be bonded with thebonding wire, an electrode in which an Al-0.5% Cu alloy was formed as afilm with a thickness of 1.0 μm on a Si substrate was used. Theobservation was performed using an optical microscope, and 200 siteswere observed for one condition. Being elliptic with large deviationfrom a perfect circle and being anisotropic in deformation weredetermined to be faulty in the crushed shape of the ball bonded part. Inthe above evaluation, a case where six or more failures occurred wasdetermined to be problematic to be marked with a symbol of “cross,” acase of four or five failures was determined to be practicable butsomewhat problematic to be marked with a symbol of “triangle,” being oneto three was determined to be no problem to be marked with a symbol of“circle,” and a case where a favorable perfect circle was obtained forall was determined to be especially excellent to be marked with a symbolof “double circle” in the column “crushed shape” in Tables 7 and 8.

[Leaning]

To a lead frame for evaluation, 100 pieces of bonding were performedwith a loop length of 5 mm and a loop height of 0.5 mm. As a method ofevaluation, a wire upright part was observed from a chip horizontaldirection, and evaluation was performed based on spacing when spacingbetween a perpendicular line passing through the center of the ballbonded part and the wire upright part was maximized (leaning spacing).If the leaning spacing was smaller than the wire diameter, leaning wasdetermined to be favorable, whereas if the leaning spacing was larger,the upright part leaned, and the leaning was determined to be faulty.One hundred bonded wires were observed with an optical microscope, andthe number of leaning failures was counted. A case where seven or morefailures occurred was determined to be problematic to be marked with asymbol of “cross,” a case of four to six failures was determined to bepracticable but somewhat problematic to be marked with a symbol of“triangle,” a case of one to three failures was determined to be noproblem to be marked with a symbol of “circle,” and a case in which nofailure occurred was determined to be excellent to be marked with asymbol of “double circle” in the column “leaning” in Tables 7 and 8.

(Evaluation Results)

The bonding wires according to Working Examples 3-1 through 3-50 eachinclude a Cu alloy core material and a Pd coating layer formed on thesurface of the Cu alloy core material, and the bonding wire contains atleast one or more elements selected from As, Te, Sn, Sb, Bi and Se, aconcentration of the elements in total is 0.1 to 100 ppm by massrelative to the entire wire. It has been revealed that with thisconfiguration the bonding wires according to Working Examples 3-1through 3-50 can achieve the reliability of the ball bonded part in theHAST test in the high-temperature and high-humidity environment of atemperature of 130° C. and a relative humidity of 85%.

In the working examples further including an alloy skin layer containingAu and Pd on the Pd coating layer, it has been revealed that excellentwedge bondability can be obtained when a thickness of the alloy skinlayer containing Au and Pd is 0.0005 to 0.050 μm.

In Working Examples 3-21 through 3-33, 3-35, 3-37, and 3-39 through3-44, it has been revealed that the high-temperature reliability of theball bonded part by the HTS evaluation is favorable because the bondingwire further contains at least one or more elements selected from Ni,Zn, Rh, In, Ir, Pt, Ga and Ge, and a concentration of each of theelements other than Pd is 0.011 to 1.2% by mass relative to the entirewire, and a concentration of Pd contained in the Cu alloy core materialis 0.05 to 1.2% by mass.

In Working Examples 3-22 through 3-26 and 3-29 through 3-32, the FABshape was favorable and the wedge bondability was favorable when thebonding wire further contains at least one or more elements selectedfrom B, P, Mg, Ca and La, and a concentration of each of the elements is1 to 100 ppm by mass relative to the entire wire.

In Working Examples 3-34 through 3-44, the wire contains As, Te, Sn, Sb,Bi and Se, and Cu was present at an outermost surface of the wire. Withthis configuration, Working Examples 3-34 through 3-44 were a symbol of“a pair of double circle” or a symbol of “double circle” in the HASTevaluation results, which revealed the effect of causing Cu to bepresent at an outermost surface.

Working Examples 4-1 to 4-15

As raw materials of a bonding wire, Cu with a purity of 99.99% by massor more and Ni, Pd, Pt, Au, P, B, Be, Fe, Mg, Ti, Zn, Ag and Si asadditive elements were used for manufacturing a Cu alloy core material;Pd with a purity of 99.99% by mass or more was used for forming acoating layer; and Au with a purity of 99.99% by mass or more was usedfor forming a skin alloy layer. Cu and the additive elements wereweighed as starting raw materials and then were heated and melted in ahigh vacuum to obtain a copper alloy ingot with a diameter of about 10mm. The ingot was then forged, rolled, and subjected to wire drawing tomanufacture a Cu alloy wire with a diameter of 500 μm. Thereafter,electroplating was performed so as to form a Pd coating layer with athickness of 1 to 3 μm on a surface of the Cu alloy wire and to form anAu skin layer with a thickness of 0.05 to 0.2 μm on a surface of thecoating layer, thus obtaining a multilayer wire. The final thicknessesof the Pd coating layer and the AuPd skin alloy layer are listed inTable 8. The position at which a concentration of Pd is 50 at % was setto be a boundary between the core material and the coating layer, andthe position at which a concentration of Au is 10 at % was set to be aboundary between the coating layer and the skin alloy layer. Continuouswire drawing was then performed with a condition of a wire drawing speedof 100 to 700 m/min and a reduction rate in area of die of 8 to 30% toobtain final wire diameters listed in Table 8. The thickness of the skinalloy layer, the maximum concentration of Au, the surface concentrationof Cu, and the thickness of the coating layer were controlled byperforming heat treatment two or three times during the wire drawing.Conditions therefor were as follows: a temperature of 500 to 700° C. anda speed of 10 to 70 m/min at a wire diameter of 200 to 250 μm; atemperature of 450 to 650° C. and a speed of 20 to 90 m/min at a wirediameter of 70 to 100 μm; and when the final wire diameter is thin,additionally a temperature of 300 to 500° C. and a speed of 30 to 100m/min at a wire diameter of 40 to 70 μm. Heat treatment was thenperformed with a condition of a temperature shown in Table 8 and a speedof 30 to 120 m/min at the final diameters. In order to diffuse Cu to thesurface, in one of heat treatments, an oxygen concentration in a heattreatment furnace was set to 0.2 to 0.7%, which was higher than a normalconcentration. This heat treatment is preferably performed last, ifpossible; this is because when wire drawing is repeated after Cu isexposed to the surface, oxidation of Cu is likely to occur. In the heattreatment other than that, the oxygen concentration in the heattreatment furnace was set to less than 0.2%, whereby a stable thickness,composition, and the like were controlled while suppressing excessiveoxidation of the skin alloy layer. Bonding wires with a diameter of 15to 25 μm were thus obtained.

The concentration analysis of the coating layer and the skin alloy layerand the concentration analysis of Ni, Pd, Pt and Au in the Cu alloy corematerial were performed using an AES apparatus while sputtering with Arions from a surface of the bonding wire in the depth direction. Thethicknesses of the coating layer and the skin alloy layer weredetermined from an obtained concentration profile in the depth direction(the unit of the depth was in terms of SiO₂). For the observation ofelement distribution, there was also performed an analysis with using anEPMA, an EDX apparatus, and the like. A region in which a concentrationof Pd was 50 at % or more and a concentration of Au was less than 10 at% was determined to be the coating layer, and a region in which aconcentration of Au was in the range of 10 at % or more on a surface ofthe coating layer was determined to be the skin alloy layer. Thethicknesses and compositions of the coating layer and the surface alloylayer are listed in Table 8. The concentrations of P, B, Be, Fe, Mg, Ti,Zn, Ag and Si in the bonding wire were measured by an ICP emissionspectrometer, an ICP mass spectrometer, and the like. As for theorientation proportion of the crystal orientation <100> angled at 15degrees or less to the wire longitudinal direction among the crystalorientations in the wire longitudinal direction in the cross-section ofthe core material in the direction perpendicular to the wire axis of thebonding wire and the average crystal grain size (μm) in thecross-section of the core material in the direction perpendicular to thewire axis, they were obtained by the same method as Working Examples 1to 59. As for 0.2% offset yield strength and ultimate strength, theywere evaluated by the same method as Working Examples 1 to 59 and astrength ratio was calculated by the above-mentioned equation (1).

For connection of a bonding wire, a commercially available automaticwire bonder was used. A ball was manufactured at a tip of the bondingwire by arc discharge immediately before bonding. The diameter of theball was selected to be 1.7 times the diameter of the bonding wire. Theatmosphere during the manufacture of the ball was nitrogen.

As objects to be bonded with the bonding wire, Al electrodes with athickness of 1 μm formed on a Si chip, and leads of a lead frame thesurface of which is plated with Pd were used. The manufactured ball wasball-bonded to the electrode heated at 260° C., followed by wedgebonding a base part of the bonding wire to the lead heated at 260° C.,and forming another ball, thus successively repeating the bonding. Aloop length was two kinds: 3 mm and 5 mm, and a loop height was twokinds: 0.3 mm and 0.5 mm.

For the wedge bondability of the bonding wire, a bondability and afishtail symmetry were evaluated. Regarding the bondability, 100 bondedparts of the bonding wire being wedge bonded were observed, and peeledbonded parts were counted as NG. Regarding the fishtail symmetry, 100bonded parts of the bonding wire being wedge bonded were observed, andtheir symmetry was evaluated. The lengths from the center of afishtail-shaped crimped part to the left end and the right end weremeasured, and the difference therebetween was 10% or more was counted asNG. Regarding the bondability and the fishtail symmetry, NG being 0 wasdetermined to be a symbol of “double circle,” being 1 to 10 wasdetermined to be a symbol of “circle,” and being 11 or more wasdetermined to be a symbol of “cross.”

For the 1st bondability (ball bondability) of the bonding wire, a HTStest, a HAST test and a FAB shape were evaluated. The HTS test wasevaluated by the same method as Working Examples 1 to 59. In order toevaluate the soundness of a ball bonding part in the HAST test, asemiconductor device in which bonding has been performed was left in ahigh-temperature, high-humidity furnace with a temperature of 130° C., arelative humidity of 85% RH, and 5 V, and the device was taken out every48 hours and was evaluated. As for the evaluation method, the electricresistance was measured, and the resistance being increased wasdetermined to be NG. Time to reach NG state being more than 480 hourswas determined to be a symbol of “double circle,” being 384 hours ormore and less than 480 hours was determined to be a symbol of “circle,”and being less than 384 hours was determined to be a symbol of “cross.”

Regarding the FAB shape, 100 FABs were manufactured on the lead frameand were observed with a SEM. A FAB being perfectly spherical wasdetermined to be OK, being eccentric or having a shrinkage cavity wasdetermined to be NG, and their numbers were counted. Regarding the FABshape, NG being 0 was determined to be a symbol of “double circle,”being 1 to 5 was determined to be a symbol of “circle,” being 6 to 10was determined to be a symbol of “triangle,” and being 11 or more wasdetermined to be a symbol of “cross.” Symbols of double circle andcircle are passing, whereas a symbol of triangle is passing but somewhatfaulty in quality. The concentrations of Ni, Pd and Pt in Table 9 (% bymass *) indicate a concentration in the Cu alloy core material.

TABLE 9 Additive element Additive Wire M_(A) M_(A) element 2 Otherdiameter Ni Pd Pt in Au Ni P B Be Fe Mg Ti Zn Ag Si No. (mm) (% by mass*) total (% by mass) (% by mass) Working 4-1 15 1.8 1.8 0.0008 Example4-2 18 0.5 0.5 0.005 0.0006 0.0004 4-3 20 1.3 1.3 0.0001 4-4 23 0.1 0.10.002 4-5 23 3.0 3.0 0.005 4-6 25 0.4 0.4 0.0011 0.0011 4-8 25 2.0 0.44-8 0.6 0.3 0.005 0.001 4-9 3.0 0.0006 0.0004 4-10 1.0 0.4 0.002 0.0010.001 4-11 0.9 0.4 0.6 0.003 0.004 0.003 4-12 1.5 4-13 0.8 4-14 1.2 4-150.7 Crystal structure <100> Mechanical characteristics Cu Proportion0.2% concentrated Coating layer Alloy skin layer of Average Offset partPd Au wire crystal Ultimate yield Strength Outermost Heat Thick- maximumThick- maximum C grain strength strength ratio surface treatment Wedgebonding ness concentration ness concentration secion size {circle around(1)} {circle around (2)} {circle around (1)}/{circle around (2)}concentration temperature Fishtail FAB No. (μm) (at %) (nm) (at %) (%)(μm) (mN/μm²) — (at %) (° C.) Bondability symmetry HTS shape HASTWorking 4-1 48 100 11 55 51 0.9 0.20 0.18 1.11 2.8 485 ⊚ ⊚ ⊚ ⊚ ⊚ Example4-2 66 100 6 34 85 1.1 0.30 0.21 1.43 2.2 475 ⊚ ⊚ ⊚ ⊚ ⊚ 4-3 66 100 22 6197 1.2 0.35 0.24 1.46 5.2 510 ⊚ ⊚ ⊚ ◯ ⊚ 4-4 90 100 4 18 55 1.0 0.23 0.211.10 3.5 510 ⊚ ◯ ⊚ ⊚ ⊚ 4-5 73 100 26 60 78 1.2 0.30 0.23 1.30 1.3 485 ⊚◯ ⊚ ◯ ⊚ 4-6 30 98 4 27 90 1.3 0.31 0.21 1.48 10 515 ⊚ ⊚ ⊚ ⊚ ⊚ 4-8 39 9912 32 65 0.9 0.23 0.19 1.21 1.4 490 ⊚ ◯ ⊚ ⊚ ⊚ 4-8 46 100 10 50 78 1.10.27 0.20 1.35 2.7 485 ⊚ ⊚ ⊚ ⊚ ⊚ 4-9 52 100 18 56 69 1.2 0.26 0.21 1.242.1 475 ⊚ ⊚ ⊚ ⊚ ⊚ 4-10 88 100 6 34 77 1.1 0.28 0.21 1.33 5.1 510 ⊚ ⊚ ⊚ ⊚⊚ 4-11 22 96 20 60 74 1.0 0.24 0.19 1.26 1.5 485 ⊚ ⊚ ⊚ ◯ ⊚ 4-12 45 100 733 65 1.2 0.20 0.17 1.18 9.8 515 ⊚ ⊚ ⊚ ⊚ ⊚ 4-13 41 100 — — 93 1.2 0.340.23 1.48 5.1 510 ⊚ ◯ ⊚ ⊚ ⊚ 4-14 60 100 — — 78 1.2 0.30 0.23 1.30 5.3510 ⊚ ◯ ⊚ ⊚ ⊚ 4-15 52 100 — — 80 1.0 0.24 0.17 1.41 5.1 510 ⊚ ◯ ⊚ ⊚ ⊚

In Working Examples 4-1 through 4-15, the Cu alloy contains one or moreelements selected from Ni, Pd and Pt (a metallic element of Group 10 ofthe Periodic Table of Elements) in an amount of 0.1 to 3.0% by mass intotal and a concentration of Cu at an outermost surface of the bondingwire is 1 to 10 at %. With this configuration, Working Examples 4-1through 4-15 exhibited excellent results in the bondability and fishtailsymmetry in the wedge bonded part and exhibited favorable results inHTS, FAB shape and HAST.

The invention claimed is:
 1. A bonding wire for a semiconductor device,the bonding wire comprising: a Cu alloy core material; and a Pd coatinglayer formed on a surface of the Cu alloy core material, wherein whenmeasuring crystal orientations on a cross-section of the core materialin a direction perpendicular to a wire axis of the bonding wire, acrystal orientation <100> angled at 15 degrees or less to a wirelongitudinal direction has a proportion of 30% or more among crystalorientations in the wire longitudinal direction, an average crystalgrain size in the cross-section of the core material in the directionperpendicular to the wire axis of the bonding wire is 0.9 μm or more and1.5 μm or less, and the bonding wire contains one or more elementsselected from Co, Rh, Ir, Ni, Pt, Ag, Au, Zn, Al, In, Sn, P, As, Sb, Bi,Se and Te.
 2. The bonding wire for a semiconductor device according toclaim 1, wherein a strength ratio defined by the following Equation (1)is 1.1 or more and 1.6 or less:Strength ratio =ultimate strength/0.2% offset yield strength  (1). 3.The bonding wire for a semiconductor device according to claim 1,wherein a thickness of the Pd coating layer is 0.015 μm or more and0.150 μm or less.
 4. The bonding wire for a semiconductor deviceaccording to claim 1, further comprising an alloy skin layer containingAu and Pd on the Pd coating layer.
 5. The bonding wire for asemiconductor device according to claim 4, wherein a thickness of thealloy skin layer containing Au and Pd is 0.050 μm or less.
 6. Thebonding wire for a semiconductor device according to claim 1, whereinthe bonding wire contains at least one element selected from Ni, Zn, Rh,In, Ir and Pt, and a concentration of the at least one element selectedfrom Ni, Zn, Rh, In, Ir and Pt in total is 0.011% by mass or more and 2%by mass or less relative to a total mass of the bonding wire.
 7. Thebonding wire for a semiconductor device according to claim 1, whereinthe bonding wire contains one or more elements selected from As, Te, Sn,Sb, Bi and Se, a concentration of the elements selected from As, Te, Sn,Sb, Bi and Se in total is 0.1 ppm by mass or more and 100 ppm by mass orless relative to a total mass of the bonding wire, and Sn≤10 ppm bymass; Sb≤10 ppm by mass; and Bi≤1 ppm by mass.
 8. The bonding wire for asemiconductor device according to claim 1, wherein the bonding wirefurther contains at least one element selected from B, P, Mg, Ca and La,and a concentration of each of the at least one element selected from B,P, Mg, Ca and La is 1 ppm by mass or more and 200 ppm by mass or lessrelative to a total mass of the bonding wire.
 9. The bonding wire for asemiconductor device according to claim 1, wherein Cu is present at anoutermost surface of the bonding wire.
 10. The bonding wire for asemiconductor device according to claim 1, wherein the Cu alloy corematerial contains a metallic element of Group 10 of the Periodic Tableof Elements in a total amount of 0.1% by mass or more and 3.0% by massor less, and a concentration of Cu at an outermost surface of the wireis 1 at % or more.
 11. The bonding wire for a semiconductor deviceaccording to claim 1, wherein the Cu alloy core material contains Pd.12. A bonding wire for a semiconductor device, the bonding wirecomprising: a Cu alloy core material; and a Pd coating layer formed on asurface of the Cu alloy core material, wherein when measuring crystalorientations on a cross-section of the core material in a directionperpendicular to a wire axis of the bonding wire, a crystal orientation<100> angled at 15 degrees or less to a wire longitudinal direction hasa proportion of 30% or more among crystal orientations in the wirelongitudinal direction, an average crystal grain size in thecross-section of the core material in the direction perpendicular to thewire axis of the bonding wire is 0.9 μm or more and 1.5 μm or less, andthe Cu alloy core material contains Pd.
 13. The bonding wire forasemiconductor device according to claim 12, wherein a strength ratiodefined by the following Equation (1) is 1.1 or more and 1.6 or less:Strength ratio =ultimate strength/0.2% offset yield strength  (1). 14.The bonding wire for a semiconductor device according to claim 12,wherein a thickness of the Pd coating layer is 0.015 μm or more and0.150 μm or less.
 15. The bonding wire for a semiconductor deviceaccording to claim 12, further comprising an alloy skin layer containingAu and Pd on the Pd coating layer.
 16. The bonding wire for asemiconductor device according to claim 15, wherein a thickness of thealloy skin layer containing Au and Pd is 0.050 μm or less.
 17. Thebonding wire for a semiconductor device according to claim 12, whereinthe bonding wire contains one or more elements selected from Co, Rh, Ir,Ni, Pt, Ag, Au, Zn, Al, In, Sn, P, As, Sb, Bi, Se and Te.
 18. Thebonding wire for a semiconductor device according to claim 17, whereinthe bonding wire contains at least one element selected from Ni, Zn, Rh,In, Jr and Pt, and a concentration of the at least one element selectedfrom Ni, Zn, Rh, In, Jr and Pt in total is 0.011% by mass or more and 2%by mass or less relative to a total mass of the bonding wire.
 19. Thebonding wire for a semiconductor device according to claim 17, whereinthe bonding wire contains one or more elements selected from As, Te, Sn,Sb, Bi and Se, a concentration of the elements selected from As, Te, Sn,Sb, Bi and Se in total is 0.1 ppm by mass or more and 100 ppm by mass orless relative to a total mass of the bonding wire, and Sn≤10 ppm bymass; Sb≤10 ppm by mass; and Bi≤1 ppm by mass.
 20. The bonding wire fora semiconductor device according to claim 12, wherein the bonding wirefurther contains at least one element selected from B, P, Mg, Ca and La,and a concentration of each of the at least one element selected from B,P, Mg, Ca and La is 1 ppm by mass or more and 200 ppm by mass or lessrelative to a total mass of the bonding wire.
 21. The bonding wire for asemiconductor device according to claim 12, wherein Cu is present at anoutermost surface of the bonding wire.
 22. The bonding wire for asemiconductor device according to claim 12, wherein the Cu alloy corematerial contains a metallic element of Group 10 of the Periodic Tableof Elements in a total amount of 0.1% by mass or more and 3.0% by massor less, and a concentration of Cu at an outermost surface of the wireis 1 at % or more.